diff --git a/src/Generator/Generator.php b/src/Generator/Generator.php
index c80c2c3f..8a0b3625 100644
--- a/src/Generator/Generator.php
+++ b/src/Generator/Generator.php
@@ -19,6 +19,7 @@
 use Laminas\Code\Generator\MethodGenerator;
 use Laminas\Code\Generator\ParameterGenerator;
 use Laminas\Code\Generator\PropertyGenerator;
+use Laminas\Code\Generator\PropertyValueGenerator;
 use Laminas\Code\Generator\TypeGenerator;
 
 class Generator
@@ -85,11 +86,83 @@ public function generateProperties(PropertyCollection $properties): array
         return $propertyGenerators;
     }
 
+    /**
+     * Generates the property holding all input properties that are not explicitly
+     * declared in the schema (for schemas combining 'properties' and 'additionalProperties').
+     */
+    public function generateAdditionalPropertiesProperty(PropertyInterface $additionalPropertiesItem): PropertyGenerator
+    {
+        $prop = new PropertyGenerator(
+            "additionalProperties",
+            new PropertyValueGenerator([], PropertyValueGenerator::TYPE_ARRAY_SHORT, PropertyValueGenerator::OUTPUT_SINGLE_LINE),
+            PropertyGenerator::FLAG_PRIVATE
+        );
+
+        $docBlock = new DocBlockGenerator(
+            "Properties from the input that are not explicitly declared in the schema",
+            null,
+            [new GenericTag("var", "array<string, " . trim($additionalPropertiesItem->typeAnnotation()) . ">")]
+        );
+        $docBlock->setWordWrap(false);
+        $prop->setDocBlock($docBlock);
+
+        if ($this->generatorRequest->isAtLeastPHP("7.4")) {
+            $prop->setType(TypeGenerator::fromTypeString("array"));
+        }
+
+        return $prop;
+    }
+
+    public function generateAdditionalPropertiesGetter(PropertyInterface $additionalPropertiesItem): MethodGenerator
+    {
+        $docBlock = new DocBlockGenerator(null, null, [
+            new ReturnTag("array<string, " . trim($additionalPropertiesItem->typeAnnotation()) . ">"),
+        ]);
+        $docBlock->setWordWrap(false);
+
+        $method = new MethodGenerator(
+            'getAdditionalProperties',
+            [],
+            MethodGenerator::FLAG_PUBLIC,
+            'return $this->additionalProperties;',
+            $docBlock
+        );
+
+        if ($this->generatorRequest->isAtLeastPHP("7.0")) {
+            $method->setReturnType("array");
+        }
+
+        return $method;
+    }
+
+    public function generateAdditionalPropertiesSetter(PropertyInterface $additionalPropertiesItem): MethodGenerator
+    {
+        $docBlock = new DocBlockGenerator(null, null, [
+            new ParamTag("additionalProperties", ["array<string, " . trim($additionalPropertiesItem->typeAnnotation()) . ">"]),
+            new ReturnTag("self"),
+        ]);
+        $docBlock->setWordWrap(false);
+
+        $method = new MethodGenerator(
+            'withAdditionalProperties',
+            [new ParameterGenerator("additionalProperties", "array")],
+            MethodGenerator::FLAG_PUBLIC,
+            "\$clone = clone \$this;\n\$clone->additionalProperties = \$additionalProperties;\n\nreturn \$clone;",
+            $docBlock
+        );
+
+        if ($this->generatorRequest->isAtLeastPHP("7.0")) {
+            $method->setReturnType("self");
+        }
+
+        return $method;
+    }
+
     /**
      * @param PropertyCollection $properties
      * @return MethodGenerator
      */
-    public function generateBuildMethod(PropertyCollection $properties): MethodGenerator
+    public function generateBuildMethod(PropertyCollection $properties, ?PropertyInterface $additionalPropertiesItem = null): MethodGenerator
     {
         $requiredProperties = $properties->filter(PropertyCollectionFilterFactory::required());
         $optionalProperties = $properties->filter(PropertyCollectionFilterFactory::optional());
@@ -148,6 +221,7 @@ public function generateBuildMethod(PropertyCollection $properties): MethodGener
             $properties->generateJSONToTypeConversionCode($inputVarName, object: true) . "\n\n" .
             '$obj = new self(' . join(", ", $constructorParams) . ');' . "\n" .
             join("\n", $assignments) . "\n" .
+            $this->generateAdditionalPropertiesCollectionCode($properties, $additionalPropertiesItem, $inputVarName) .
             'return $obj;',
             $docBlock
         );
@@ -159,11 +233,32 @@ public function generateBuildMethod(PropertyCollection $properties): MethodGener
         return $method;
     }
 
+    private function generateAdditionalPropertiesCollectionCode(PropertyCollection $properties, ?PropertyInterface $additionalPropertiesItem, string $inputVarName): string
+    {
+        if ($additionalPropertiesItem === null) {
+            return "";
+        }
+
+        $declaredKeys = [];
+        foreach ($properties as $property) {
+            $declaredKeys[] = var_export($property->key(), true);
+        }
+
+        $mapping = $additionalPropertiesItem->generateInputMappingExpr('$value');
+
+        return "foreach (get_object_vars(\$$inputVarName) as \$key => \$value) {\n" .
+            "    if (in_array(\$key, [" . join(", ", $declaredKeys) . "], true)) {\n" .
+            "        continue;\n" .
+            "    }\n" .
+            "    \$obj->additionalProperties[\$key] = {$mapping};\n" .
+            "}\n";
+    }
+
     /**
      * @param PropertyCollection $properties
      * @return MethodGenerator
      */
-    public function generateToJSONMethod(PropertyCollection $properties): MethodGenerator
+    public function generateToJSONMethod(PropertyCollection $properties, ?PropertyInterface $additionalPropertiesItem = null): MethodGenerator
     {
         $docBlock = new DocBlockGenerator(
             "Converts this object back to a simple array that can be JSON-serialized",
@@ -172,11 +267,24 @@ public function generateToJSONMethod(PropertyCollection $properties): MethodGene
         );
         $docBlock->setWordWrap(false);
 
+        $additionalPropertiesCode = "";
+        if ($additionalPropertiesItem !== null) {
+            $mapping = $additionalPropertiesItem->generateOutputMappingExpr('$value');
+
+            // Additional properties are written first so that declared properties
+            // always win in case of a key collision.
+            $additionalPropertiesCode =
+                "foreach (\$this->additionalProperties as \$key => \$value) {\n" .
+                "    \$output[\$key] = {$mapping};\n" .
+                "}\n";
+        }
+
         $method = new MethodGenerator(
             'toJson',
             [],
             MethodGenerator::FLAG_PUBLIC,
             '$output = [];' . "\n" .
+            $additionalPropertiesCode .
             $properties->generateTypeToJSONConversionCode('output') . "\n\n" .
             'return $output;',
             $docBlock
@@ -241,7 +349,7 @@ public function generateValidateMethod(): MethodGenerator
      * @param PropertyCollection $properties
      * @return MethodGenerator
      */
-    public function generateCloneMethod(PropertyCollection $properties): MethodGenerator
+    public function generateCloneMethod(PropertyCollection $properties, ?PropertyInterface $additionalPropertiesItem = null): MethodGenerator
     {
         $clones = [];
 
@@ -252,6 +360,15 @@ public function generateCloneMethod(PropertyCollection $properties): MethodGener
             }
         }
 
+        if ($additionalPropertiesItem !== null) {
+            $cloneExpr = $additionalPropertiesItem->generateCloneExpr('$value');
+            if ($cloneExpr !== '$value') {
+                $clones[] = $this->generatorRequest->isAtLeastPHP("7.4")
+                    ? "\$this->additionalProperties = array_map(fn (\$value) => {$cloneExpr}, \$this->additionalProperties);"
+                    : "\$this->additionalProperties = array_map(function (\$value) { return {$cloneExpr}; }, \$this->additionalProperties);";
+            }
+        }
+
         return new MethodGenerator(
             '__clone',
             [],
diff --git a/src/Generator/NamespaceInferrer.php b/src/Generator/NamespaceInferrer.php
index c9add02d..9c83ea32 100644
--- a/src/Generator/NamespaceInferrer.php
+++ b/src/Generator/NamespaceInferrer.php
@@ -25,7 +25,7 @@ public function inferNamespaceFromTargetDirectory(string $directory): string
         }
 
         if ($directory[0] !== "/") {
-            $directory = $workingDirectory . PATH_SEPARATOR . $directory;
+            $directory = $workingDirectory . DIRECTORY_SEPARATOR . $directory;
         }
 
         list($root, $composer) = $this->getComposerJSONForDirectory($directory);
diff --git a/src/Generator/Property/NestedObjectProperty.php b/src/Generator/Property/NestedObjectProperty.php
index 8849ef1e..7f06fe21 100644
--- a/src/Generator/Property/NestedObjectProperty.php
+++ b/src/Generator/Property/NestedObjectProperty.php
@@ -13,8 +13,12 @@ public static function canHandleSchema(array $schema): bool
     {
         $isObject = isset($schema["type"]) && $schema["type"] === "object" || isset($schema["properties"]);
         $isAssociativeArray = isset($schema["additionalProperties"]) && is_array($schema["additionalProperties"]);
+        $hasProperties = isset($schema["properties"]) && count($schema["properties"]) > 0;
 
-        return $isObject && !$isAssociativeArray;
+        // Schemas with declared properties are generated as classes, even when they
+        // also allow additional properties; purely map-like schemas (only
+        // 'additionalProperties') are handled by the array property types instead.
+        return $isObject && ($hasProperties || !$isAssociativeArray);
     }
 
     public function isComplex(): bool
diff --git a/src/Generator/Property/OptionalPropertyDecorator.php b/src/Generator/Property/OptionalPropertyDecorator.php
index acbf9210..166e9172 100644
--- a/src/Generator/Property/OptionalPropertyDecorator.php
+++ b/src/Generator/Property/OptionalPropertyDecorator.php
@@ -71,6 +71,12 @@ public function convertTypeToJSON(string $outputVarName = 'output'): string
         $name  = $this->inner->name();
         $inner = $this->inner->convertTypeToJSON($outputVarName);
 
+        // Properties with a default value are declared non-nullable and initialized
+        // with their default, so isset() on them would always be true.
+        if (isset($this->schema()["default"])) {
+            return $inner;
+        }
+
         return "if (isset(\$this->{$name})) {\n" . $this->indentCode($inner, 1) . "\n}";
     }
 
@@ -136,6 +142,11 @@ public function cloneProperty(): ?string
         $inner = $this->inner->cloneProperty();
 
         if ($inner !== null) {
+            // See convertTypeToJSON(): properties with a default value are always set.
+            if (isset($this->schema()["default"])) {
+                return $inner;
+            }
+
             return "if (isset(\$this->{$name})) {\n" . $this->indentCode($inner, 1) . "\n}";
         }
 
diff --git a/src/Generator/PropertyBuilder.php b/src/Generator/PropertyBuilder.php
index b74c06d6..a81bad92 100644
--- a/src/Generator/PropertyBuilder.php
+++ b/src/Generator/PropertyBuilder.php
@@ -51,8 +51,6 @@ class PropertyBuilder
      */
     public static function buildPropertyFromSchema(GeneratorRequest $req, string $name, array $definition, bool $isRequired): PropertyInterface
     {
-        self::testInvariants($definition);
-
         foreach (self::$propertyTypes as $propertyType) {
             if ($propertyType::canHandleSchema($definition)) {
                 /** @var PropertyInterface $property */
@@ -71,14 +69,4 @@ public static function buildPropertyFromSchema(GeneratorRequest $req, string $na
         /** @psalm-suppress PossiblyFalseOperand */
         throw new GeneratorException("cannot map type " . json_encode($definition));
     }
-
-    private static function testInvariants(array $definition): void
-    {
-        $hasAdditionalProperties = isset($definition["additionalProperties"]) && is_array($definition["additionalProperties"]) && count($definition["additionalProperties"]) > 0;
-        $hasProperties = isset($definition["properties"]) && is_array($definition["properties"]) && count($definition["properties"]) > 0;
-
-        if ($hasProperties && $hasAdditionalProperties) {
-            throw new GeneratorException("using 'properties' and 'additionalProperties' in the same schema is currently not supported.");
-        }
-    }
 }
\ No newline at end of file
diff --git a/src/Generator/SchemaToClass.php b/src/Generator/SchemaToClass.php
index 91851cff..7e0cd15d 100644
--- a/src/Generator/SchemaToClass.php
+++ b/src/Generator/SchemaToClass.php
@@ -77,10 +77,14 @@ public function schemaToClass(GeneratorRequest $req): void
             }
         }
 
+        $additionalPropertiesItem = $this->buildAdditionalPropertiesItem($req, $schema);
+
         foreach ($propertiesFromSchema as $property) {
             $property->generateSubTypes($this);
         }
 
+        $additionalPropertiesItem?->generateSubTypes($this);
+
         $codeGenerator = new Generator($req);
 
         $properties = [
@@ -88,14 +92,22 @@ public function schemaToClass(GeneratorRequest $req): void
             ...$codeGenerator->generateProperties($propertiesFromSchema),
         ];
 
+        if ($additionalPropertiesItem !== null) {
+            $properties[] = $codeGenerator->generateAdditionalPropertiesProperty($additionalPropertiesItem);
+        }
+
         $methods = [
             $codeGenerator->generateConstructor($propertiesFromSchema),
             ...$codeGenerator->generateGetterMethods($propertiesFromSchema),
             ...$codeGenerator->generateSetterMethods($propertiesFromSchema),
-            $codeGenerator->generateBuildMethod($propertiesFromSchema),
-            $codeGenerator->generateToJSONMethod($propertiesFromSchema),
+            ...($additionalPropertiesItem !== null ? [
+                $codeGenerator->generateAdditionalPropertiesGetter($additionalPropertiesItem),
+                $codeGenerator->generateAdditionalPropertiesSetter($additionalPropertiesItem),
+            ] : []),
+            $codeGenerator->generateBuildMethod($propertiesFromSchema, $additionalPropertiesItem),
+            $codeGenerator->generateToJSONMethod($propertiesFromSchema, $additionalPropertiesItem),
             $codeGenerator->generateValidateMethod(),
-            $codeGenerator->generateCloneMethod($propertiesFromSchema),
+            $codeGenerator->generateCloneMethod($propertiesFromSchema, $additionalPropertiesItem),
         ];
 
         $cls = new ClassGenerator(
@@ -131,4 +143,28 @@ public function schemaToClass(GeneratorRequest $req): void
         $this->writer->writeFile($filename, $content);
     }
 
+    /**
+     * Builds a pseudo-property representing the value type of 'additionalProperties'
+     * for schemas that combine 'properties' and 'additionalProperties'. Returns null
+     * when the schema does not use this combination; purely map-like schemas (only
+     * 'additionalProperties') are represented as plain array properties instead.
+     *
+     * @throws GeneratorException
+     */
+    private function buildAdditionalPropertiesItem(GeneratorRequest $req, array $schema): ?Property\PropertyInterface
+    {
+        $hasProperties           = isset($schema["properties"]) && count($schema["properties"]) > 0;
+        $hasAdditionalProperties = isset($schema["additionalProperties"]) && is_array($schema["additionalProperties"]) && count($schema["additionalProperties"]) > 0;
+
+        if (!$hasProperties || !$hasAdditionalProperties) {
+            return null;
+        }
+
+        if (isset($schema["properties"]["additionalProperties"])) {
+            throw new GeneratorException("schemas using 'additionalProperties' together with a regular property named 'additionalProperties' are not supported");
+        }
+
+        return PropertyBuilder::buildPropertyFromSchema($req, "additionalPropertiesItem", $schema["additionalProperties"], true);
+    }
+
 }
diff --git a/src/Spec/Specification.php b/src/Spec/Specification.php
index 5abd6980..f7e7e8e6 100644
--- a/src/Spec/Specification.php
+++ b/src/Spec/Specification.php
@@ -123,7 +123,7 @@ public function __construct(array $files)
     /**
      * @return int|string|null
      */
-    public function getTargetPHPVersion() : int|string|null
+    public function getTargetPHPVersion(): int|string|null
     {
         return $this->targetPHPVersion;
     }
@@ -131,7 +131,7 @@ public function getTargetPHPVersion() : int|string|null
     /**
      * @return SpecificationFilesItem[]
      */
-    public function getFiles() : array
+    public function getFiles(): array
     {
         return $this->files;
     }
@@ -139,7 +139,7 @@ public function getFiles() : array
     /**
      * @return SpecificationOptions|null
      */
-    public function getOptions() : ?SpecificationOptions
+    public function getOptions(): ?SpecificationOptions
     {
         return $this->options ?? null;
     }
@@ -148,7 +148,7 @@ public function getOptions() : ?SpecificationOptions
      * @param int|string $targetPHPVersion
      * @return self
      */
-    public function withTargetPHPVersion(int|string $targetPHPVersion) : self
+    public function withTargetPHPVersion(int|string $targetPHPVersion): self
     {
         $clone = clone $this;
         $clone->targetPHPVersion = $targetPHPVersion;
@@ -159,7 +159,7 @@ public function withTargetPHPVersion(int|string $targetPHPVersion) : self
     /**
      * @return self
      */
-    public function withoutTargetPHPVersion() : self
+    public function withoutTargetPHPVersion(): self
     {
         $clone = clone $this;
         unset($clone->targetPHPVersion);
@@ -171,7 +171,7 @@ public function withoutTargetPHPVersion() : self
      * @param SpecificationFilesItem[] $files
      * @return self
      */
-    public function withFiles(array $files) : self
+    public function withFiles(array $files): self
     {
         $clone = clone $this;
         $clone->files = $files;
@@ -183,7 +183,7 @@ public function withFiles(array $files) : self
      * @param SpecificationOptions $options
      * @return self
      */
-    public function withOptions(SpecificationOptions $options) : self
+    public function withOptions(SpecificationOptions $options): self
     {
         $clone = clone $this;
         $clone->options = $options;
@@ -194,7 +194,7 @@ public function withOptions(SpecificationOptions $options) : self
     /**
      * @return self
      */
-    public function withoutOptions() : self
+    public function withoutOptions(): self
     {
         $clone = clone $this;
         unset($clone->options);
@@ -210,7 +210,7 @@ public function withoutOptions() : self
      * @return Specification Created instance
      * @throws \InvalidArgumentException
      */
-    public static function buildFromInput(array|object $input, bool $validate = true) : Specification
+    public static function buildFromInput(array|object $input, bool $validate = true): Specification
     {
         $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
         if ($validate) {
@@ -241,7 +241,7 @@ public static function buildFromInput(array|object $input, bool $validate = true
      *
      * @return array Converted array
      */
-    public function toJson() : array
+    public function toJson(): array
     {
         $output = [];
         if (isset($this->targetPHPVersion)) {
@@ -265,7 +265,7 @@ public function toJson() : array
      * @return bool Validation result
      * @throws \InvalidArgumentException
      */
-    public static function validateInput(array|object $input, bool $return = false) : bool
+    public static function validateInput(array|object $input, bool $return = false): bool
     {
         $validator = new \JsonSchema\Validator();
         $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
diff --git a/src/Spec/SpecificationFilesItem.php b/src/Spec/SpecificationFilesItem.php
index 5bc34f2f..4b5069a2 100644
--- a/src/Spec/SpecificationFilesItem.php
+++ b/src/Spec/SpecificationFilesItem.php
@@ -68,7 +68,7 @@ public function __construct(string $input, string $className, string $targetDire
     /**
      * @return string
      */
-    public function getInput() : string
+    public function getInput(): string
     {
         return $this->input;
     }
@@ -76,7 +76,7 @@ public function getInput() : string
     /**
      * @return string
      */
-    public function getClassName() : string
+    public function getClassName(): string
     {
         return $this->className;
     }
@@ -84,7 +84,7 @@ public function getClassName() : string
     /**
      * @return string
      */
-    public function getTargetDirectory() : string
+    public function getTargetDirectory(): string
     {
         return $this->targetDirectory;
     }
@@ -92,7 +92,7 @@ public function getTargetDirectory() : string
     /**
      * @return string|null
      */
-    public function getTargetNamespace() : ?string
+    public function getTargetNamespace(): ?string
     {
         return $this->targetNamespace ?? null;
     }
@@ -101,7 +101,7 @@ public function getTargetNamespace() : ?string
      * @param string $input
      * @return self
      */
-    public function withInput(string $input) : self
+    public function withInput(string $input): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($input, self::$internalValidationSchema['properties']['input']);
@@ -119,7 +119,7 @@ public function withInput(string $input) : self
      * @param string $className
      * @return self
      */
-    public function withClassName(string $className) : self
+    public function withClassName(string $className): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($className, self::$internalValidationSchema['properties']['className']);
@@ -137,7 +137,7 @@ public function withClassName(string $className) : self
      * @param string $targetDirectory
      * @return self
      */
-    public function withTargetDirectory(string $targetDirectory) : self
+    public function withTargetDirectory(string $targetDirectory): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($targetDirectory, self::$internalValidationSchema['properties']['targetDirectory']);
@@ -155,7 +155,7 @@ public function withTargetDirectory(string $targetDirectory) : self
      * @param string $targetNamespace
      * @return self
      */
-    public function withTargetNamespace(string $targetNamespace) : self
+    public function withTargetNamespace(string $targetNamespace): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($targetNamespace, self::$internalValidationSchema['properties']['targetNamespace']);
@@ -172,7 +172,7 @@ public function withTargetNamespace(string $targetNamespace) : self
     /**
      * @return self
      */
-    public function withoutTargetNamespace() : self
+    public function withoutTargetNamespace(): self
     {
         $clone = clone $this;
         unset($clone->targetNamespace);
@@ -188,7 +188,7 @@ public function withoutTargetNamespace() : self
      * @return SpecificationFilesItem Created instance
      * @throws \InvalidArgumentException
      */
-    public static function buildFromInput(array|object $input2, bool $validate = true) : SpecificationFilesItem
+    public static function buildFromInput(array|object $input2, bool $validate = true): SpecificationFilesItem
     {
         $input2 = is_array($input2) ? \JsonSchema\Validator::arrayToObjectRecursive($input2) : $input2;
         if ($validate) {
@@ -213,7 +213,7 @@ public static function buildFromInput(array|object $input2, bool $validate = tru
      *
      * @return array Converted array
      */
-    public function toJson() : array
+    public function toJson(): array
     {
         $output = [];
         $output['input'] = $this->input;
@@ -234,7 +234,7 @@ public function toJson() : array
      * @return bool Validation result
      * @throws \InvalidArgumentException
      */
-    public static function validateInput(array|object $input, bool $return = false) : bool
+    public static function validateInput(array|object $input, bool $return = false): bool
     {
         $validator = new \JsonSchema\Validator();
         $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
diff --git a/src/Spec/SpecificationOptions.php b/src/Spec/SpecificationOptions.php
index 952396a4..41146ca8 100644
--- a/src/Spec/SpecificationOptions.php
+++ b/src/Spec/SpecificationOptions.php
@@ -90,7 +90,7 @@ public function __construct()
     /**
      * @return bool
      */
-    public function getDisableStrictTypes() : bool
+    public function getDisableStrictTypes(): bool
     {
         return $this->disableStrictTypes;
     }
@@ -98,7 +98,7 @@ public function getDisableStrictTypes() : bool
     /**
      * @return bool
      */
-    public function getTreatValuesWithDefaultAsOptional() : bool
+    public function getTreatValuesWithDefaultAsOptional(): bool
     {
         return $this->treatValuesWithDefaultAsOptional;
     }
@@ -106,7 +106,7 @@ public function getTreatValuesWithDefaultAsOptional() : bool
     /**
      * @return bool
      */
-    public function getInlineAllofReferences() : bool
+    public function getInlineAllofReferences(): bool
     {
         return $this->inlineAllofReferences;
     }
@@ -114,7 +114,7 @@ public function getInlineAllofReferences() : bool
     /**
      * @return int|string
      */
-    public function getTargetPHPVersion() : int|string
+    public function getTargetPHPVersion(): int|string
     {
         return $this->targetPHPVersion;
     }
@@ -122,7 +122,7 @@ public function getTargetPHPVersion() : int|string
     /**
      * @return string
      */
-    public function getNewValidatorClassExpr() : string
+    public function getNewValidatorClassExpr(): string
     {
         return $this->newValidatorClassExpr;
     }
@@ -131,7 +131,7 @@ public function getNewValidatorClassExpr() : string
      * @param bool $disableStrictTypes
      * @return self
      */
-    public function withDisableStrictTypes(bool $disableStrictTypes) : self
+    public function withDisableStrictTypes(bool $disableStrictTypes): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($disableStrictTypes, self::$internalValidationSchema['properties']['disableStrictTypes']);
@@ -148,7 +148,7 @@ public function withDisableStrictTypes(bool $disableStrictTypes) : self
     /**
      * @return self
      */
-    public function withoutDisableStrictTypes() : self
+    public function withoutDisableStrictTypes(): self
     {
         $clone = clone $this;
         $clone->disableStrictTypes = false;
@@ -160,7 +160,7 @@ public function withoutDisableStrictTypes() : self
      * @param bool $treatValuesWithDefaultAsOptional
      * @return self
      */
-    public function withTreatValuesWithDefaultAsOptional(bool $treatValuesWithDefaultAsOptional) : self
+    public function withTreatValuesWithDefaultAsOptional(bool $treatValuesWithDefaultAsOptional): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($treatValuesWithDefaultAsOptional, self::$internalValidationSchema['properties']['treatValuesWithDefaultAsOptional']);
@@ -177,7 +177,7 @@ public function withTreatValuesWithDefaultAsOptional(bool $treatValuesWithDefaul
     /**
      * @return self
      */
-    public function withoutTreatValuesWithDefaultAsOptional() : self
+    public function withoutTreatValuesWithDefaultAsOptional(): self
     {
         $clone = clone $this;
         $clone->treatValuesWithDefaultAsOptional = false;
@@ -189,7 +189,7 @@ public function withoutTreatValuesWithDefaultAsOptional() : self
      * @param bool $inlineAllofReferences
      * @return self
      */
-    public function withInlineAllofReferences(bool $inlineAllofReferences) : self
+    public function withInlineAllofReferences(bool $inlineAllofReferences): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($inlineAllofReferences, self::$internalValidationSchema['properties']['inlineAllofReferences']);
@@ -206,7 +206,7 @@ public function withInlineAllofReferences(bool $inlineAllofReferences) : self
     /**
      * @return self
      */
-    public function withoutInlineAllofReferences() : self
+    public function withoutInlineAllofReferences(): self
     {
         $clone = clone $this;
         $clone->inlineAllofReferences = false;
@@ -218,7 +218,7 @@ public function withoutInlineAllofReferences() : self
      * @param int|string $targetPHPVersion
      * @return self
      */
-    public function withTargetPHPVersion(int|string $targetPHPVersion) : self
+    public function withTargetPHPVersion(int|string $targetPHPVersion): self
     {
         $clone = clone $this;
         $clone->targetPHPVersion = $targetPHPVersion;
@@ -229,7 +229,7 @@ public function withTargetPHPVersion(int|string $targetPHPVersion) : self
     /**
      * @return self
      */
-    public function withoutTargetPHPVersion() : self
+    public function withoutTargetPHPVersion(): self
     {
         $clone = clone $this;
         $clone->targetPHPVersion = '8.2.0';
@@ -241,7 +241,7 @@ public function withoutTargetPHPVersion() : self
      * @param string $newValidatorClassExpr
      * @return self
      */
-    public function withNewValidatorClassExpr(string $newValidatorClassExpr) : self
+    public function withNewValidatorClassExpr(string $newValidatorClassExpr): self
     {
         $validator = new \JsonSchema\Validator();
         $validator->validate($newValidatorClassExpr, self::$internalValidationSchema['properties']['newValidatorClassExpr']);
@@ -258,7 +258,7 @@ public function withNewValidatorClassExpr(string $newValidatorClassExpr) : self
     /**
      * @return self
      */
-    public function withoutNewValidatorClassExpr() : self
+    public function withoutNewValidatorClassExpr(): self
     {
         $clone = clone $this;
         $clone->newValidatorClassExpr = 'new \\JsonSchema\\Validator()';
@@ -274,7 +274,7 @@ public function withoutNewValidatorClassExpr() : self
      * @return SpecificationOptions Created instance
      * @throws \InvalidArgumentException
      */
-    public static function buildFromInput(array|object $input, bool $validate = true) : SpecificationOptions
+    public static function buildFromInput(array|object $input, bool $validate = true): SpecificationOptions
     {
         $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
         if ($validate) {
@@ -319,26 +319,16 @@ public static function buildFromInput(array|object $input, bool $validate = true
      *
      * @return array Converted array
      */
-    public function toJson() : array
+    public function toJson(): array
     {
         $output = [];
-        if (isset($this->disableStrictTypes)) {
-            $output['disableStrictTypes'] = $this->disableStrictTypes;
-        }
-        if (isset($this->treatValuesWithDefaultAsOptional)) {
-            $output['treatValuesWithDefaultAsOptional'] = $this->treatValuesWithDefaultAsOptional;
-        }
-        if (isset($this->inlineAllofReferences)) {
-            $output['inlineAllofReferences'] = $this->inlineAllofReferences;
-        }
-        if (isset($this->targetPHPVersion)) {
-            $output['targetPHPVersion'] = match (true) {
-                is_int($this->targetPHPVersion), is_string($this->targetPHPVersion) => $this->targetPHPVersion,
-            };
-        }
-        if (isset($this->newValidatorClassExpr)) {
-            $output['newValidatorClassExpr'] = $this->newValidatorClassExpr;
-        }
+        $output['disableStrictTypes'] = $this->disableStrictTypes;
+        $output['treatValuesWithDefaultAsOptional'] = $this->treatValuesWithDefaultAsOptional;
+        $output['inlineAllofReferences'] = $this->inlineAllofReferences;
+        $output['targetPHPVersion'] = match (true) {
+            is_int($this->targetPHPVersion), is_string($this->targetPHPVersion) => $this->targetPHPVersion,
+        };
+        $output['newValidatorClassExpr'] = $this->newValidatorClassExpr;
 
         return $output;
     }
@@ -351,7 +341,7 @@ public function toJson() : array
      * @return bool Validation result
      * @throws \InvalidArgumentException
      */
-    public static function validateInput(array|object $input, bool $return = false) : bool
+    public static function validateInput(array|object $input, bool $return = false): bool
     {
         $validator = new \JsonSchema\Validator();
         $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
@@ -369,11 +359,9 @@ public static function validateInput(array|object $input, bool $return = false)
 
     public function __clone()
     {
-        if (isset($this->targetPHPVersion)) {
-            $this->targetPHPVersion = match (true) {
-                is_int($this->targetPHPVersion), is_string($this->targetPHPVersion) => $this->targetPHPVersion,
-            };
-        }
+        $this->targetPHPVersion = match (true) {
+            is_int($this->targetPHPVersion), is_string($this->targetPHPVersion) => $this->targetPHPVersion,
+        };
     }
 }
 
diff --git a/tests/Generator/Fixtures/DefaultValue/Output/Foo.php b/tests/Generator/Fixtures/DefaultValue/Output/Foo.php
index af69ac3d..6db0dc69 100644
--- a/tests/Generator/Fixtures/DefaultValue/Output/Foo.php
+++ b/tests/Generator/Fixtures/DefaultValue/Output/Foo.php
@@ -157,12 +157,8 @@ public static function buildFromInput(array|object $input, bool $validate = true
     public function toJson(): array
     {
         $output = [];
-        if (isset($this->limit)) {
-            $output['limit'] = $this->limit;
-        }
-        if (isset($this->skip)) {
-            $output['skip'] = $this->skip;
-        }
+        $output['limit'] = $this->limit;
+        $output['skip'] = $this->skip;
 
         return $output;
     }
diff --git a/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/Output/Foo.php b/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/Output/Foo.php
new file mode 100644
index 00000000..c691a034
--- /dev/null
+++ b/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/Output/Foo.php
@@ -0,0 +1,175 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ns\PropsWithAdditionalObjectProps;
+
+class Foo
+{
+    /**
+     * Schema used to validate input for creating instances of this class
+     *
+     * @var array
+     */
+    private static array $internalValidationSchema = [
+        'type' => 'object',
+        'required' => [
+            'name',
+        ],
+        'properties' => [
+            'name' => [
+                'type' => 'string',
+            ],
+        ],
+        'additionalProperties' => [
+            'type' => 'object',
+            'required' => [
+                'value',
+            ],
+            'properties' => [
+                'value' => [
+                    'type' => 'string',
+                ],
+            ],
+        ],
+    ];
+
+    /**
+     * @var string
+     */
+    private string $name;
+
+    /**
+     * Properties from the input that are not explicitly declared in the schema
+     *
+     * @var array<string, FooAdditionalPropertiesItem>
+     */
+    private array $additionalProperties = [];
+
+    /**
+     * @param string $name
+     */
+    public function __construct(string $name)
+    {
+        $this->name = $name;
+    }
+
+    /**
+     * @return string
+     */
+    public function getName(): string
+    {
+        return $this->name;
+    }
+
+    /**
+     * @param string $name
+     * @return self
+     */
+    public function withName(string $name): self
+    {
+        $validator = new \JsonSchema\Validator();
+        $validator->validate($name, self::$internalValidationSchema['properties']['name']);
+        if (!$validator->isValid()) {
+            throw new \InvalidArgumentException($validator->getErrors()[0]['message']);
+        }
+
+        $clone = clone $this;
+        $clone->name = $name;
+
+        return $clone;
+    }
+
+    /**
+     * @return array<string, FooAdditionalPropertiesItem>
+     */
+    public function getAdditionalProperties(): array
+    {
+        return $this->additionalProperties;
+    }
+
+    /**
+     * @param array<string, FooAdditionalPropertiesItem> $additionalProperties
+     * @return self
+     */
+    public function withAdditionalProperties(array $additionalProperties): self
+    {
+        $clone = clone $this;
+        $clone->additionalProperties = $additionalProperties;
+
+        return $clone;
+    }
+
+    /**
+     * Builds a new instance from an input array
+     *
+     * @param array|object $input Input data
+     * @param bool $validate Set this to false to skip validation; use at own risk
+     * @return Foo Created instance
+     * @throws \InvalidArgumentException
+     */
+    public static function buildFromInput(array|object $input, bool $validate = true): Foo
+    {
+        $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
+        if ($validate) {
+            static::validateInput($input);
+        }
+
+        $name = $input->{'name'};
+
+        $obj = new self($name);
+
+        foreach (get_object_vars($input) as $key => $value) {
+            if (in_array($key, ['name'], true)) {
+                continue;
+            }
+            $obj->additionalProperties[$key] = FooAdditionalPropertiesItem::buildFromInput($value, validate: $validate);
+        }
+        return $obj;
+    }
+
+    /**
+     * Converts this object back to a simple array that can be JSON-serialized
+     *
+     * @return array Converted array
+     */
+    public function toJson(): array
+    {
+        $output = [];
+        foreach ($this->additionalProperties as $key => $value) {
+            $output[$key] = ($value)->toJson();
+        }
+        $output['name'] = $this->name;
+
+        return $output;
+    }
+
+    /**
+     * Validates an input array
+     *
+     * @param array|object $input Input data
+     * @param bool $return Return instead of throwing errors
+     * @return bool Validation result
+     * @throws \InvalidArgumentException
+     */
+    public static function validateInput(array|object $input, bool $return = false): bool
+    {
+        $validator = new \JsonSchema\Validator();
+        $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
+        $validator->validate($input, self::$internalValidationSchema);
+
+        if (!$validator->isValid() && !$return) {
+            $errors = array_map(function(array $e): string {
+                return $e["property"] . ": " . $e["message"];
+            }, $validator->getErrors());
+            throw new \InvalidArgumentException(join(", ", $errors));
+        }
+
+        return $validator->isValid();
+    }
+
+    public function __clone()
+    {
+        $this->additionalProperties = array_map(fn ($value) => clone $value, $this->additionalProperties);
+    }
+}
\ No newline at end of file
diff --git a/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/Output/FooAdditionalPropertiesItem.php b/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/Output/FooAdditionalPropertiesItem.php
new file mode 100644
index 00000000..45e4f67b
--- /dev/null
+++ b/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/Output/FooAdditionalPropertiesItem.php
@@ -0,0 +1,127 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ns\PropsWithAdditionalObjectProps;
+
+class FooAdditionalPropertiesItem
+{
+    /**
+     * Schema used to validate input for creating instances of this class
+     *
+     * @var array
+     */
+    private static array $internalValidationSchema = [
+        'type' => 'object',
+        'required' => [
+            'value',
+        ],
+        'properties' => [
+            'value' => [
+                'type' => 'string',
+            ],
+        ],
+    ];
+
+    /**
+     * @var string
+     */
+    private string $value;
+
+    /**
+     * @param string $value
+     */
+    public function __construct(string $value)
+    {
+        $this->value = $value;
+    }
+
+    /**
+     * @return string
+     */
+    public function getValue(): string
+    {
+        return $this->value;
+    }
+
+    /**
+     * @param string $value
+     * @return self
+     */
+    public function withValue(string $value): self
+    {
+        $validator = new \JsonSchema\Validator();
+        $validator->validate($value, self::$internalValidationSchema['properties']['value']);
+        if (!$validator->isValid()) {
+            throw new \InvalidArgumentException($validator->getErrors()[0]['message']);
+        }
+
+        $clone = clone $this;
+        $clone->value = $value;
+
+        return $clone;
+    }
+
+    /**
+     * Builds a new instance from an input array
+     *
+     * @param array|object $input Input data
+     * @param bool $validate Set this to false to skip validation; use at own risk
+     * @return FooAdditionalPropertiesItem Created instance
+     * @throws \InvalidArgumentException
+     */
+    public static function buildFromInput(array|object $input, bool $validate = true): FooAdditionalPropertiesItem
+    {
+        $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
+        if ($validate) {
+            static::validateInput($input);
+        }
+
+        $value = $input->{'value'};
+
+        $obj = new self($value);
+
+        return $obj;
+    }
+
+    /**
+     * Converts this object back to a simple array that can be JSON-serialized
+     *
+     * @return array Converted array
+     */
+    public function toJson(): array
+    {
+        $output = [];
+        $output['value'] = $this->value;
+
+        return $output;
+    }
+
+    /**
+     * Validates an input array
+     *
+     * @param array|object $input Input data
+     * @param bool $return Return instead of throwing errors
+     * @return bool Validation result
+     * @throws \InvalidArgumentException
+     */
+    public static function validateInput(array|object $input, bool $return = false): bool
+    {
+        $validator = new \JsonSchema\Validator();
+        $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
+        $validator->validate($input, self::$internalValidationSchema);
+
+        if (!$validator->isValid() && !$return) {
+            $errors = array_map(function(array $e): string {
+                return $e["property"] . ": " . $e["message"];
+            }, $validator->getErrors());
+            throw new \InvalidArgumentException(join(", ", $errors));
+        }
+
+        return $validator->isValid();
+    }
+
+    public function __clone()
+    {
+    }
+}
\ No newline at end of file
diff --git a/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/schema.yaml b/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/schema.yaml
new file mode 100644
index 00000000..e067add1
--- /dev/null
+++ b/tests/Generator/Fixtures/PropsWithAdditionalObjectProps/schema.yaml
@@ -0,0 +1,13 @@
+type: object
+required:
+  - name
+properties:
+  name:
+    type: string
+additionalProperties:
+  type: object
+  required:
+    - value
+  properties:
+    value:
+      type: string
diff --git a/tests/Generator/Fixtures/PropsWithAdditionalProps/Output/Foo.php b/tests/Generator/Fixtures/PropsWithAdditionalProps/Output/Foo.php
new file mode 100644
index 00000000..b36ae31d
--- /dev/null
+++ b/tests/Generator/Fixtures/PropsWithAdditionalProps/Output/Foo.php
@@ -0,0 +1,166 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Ns\PropsWithAdditionalProps;
+
+class Foo
+{
+    /**
+     * Schema used to validate input for creating instances of this class
+     *
+     * @var array
+     */
+    private static array $internalValidationSchema = [
+        'type' => 'object',
+        'required' => [
+            'reason',
+        ],
+        'properties' => [
+            'reason' => [
+                'type' => 'string',
+            ],
+        ],
+        'additionalProperties' => [
+            'type' => 'string',
+        ],
+    ];
+
+    /**
+     * @var string
+     */
+    private string $reason;
+
+    /**
+     * Properties from the input that are not explicitly declared in the schema
+     *
+     * @var array<string, string>
+     */
+    private array $additionalProperties = [];
+
+    /**
+     * @param string $reason
+     */
+    public function __construct(string $reason)
+    {
+        $this->reason = $reason;
+    }
+
+    /**
+     * @return string
+     */
+    public function getReason(): string
+    {
+        return $this->reason;
+    }
+
+    /**
+     * @param string $reason
+     * @return self
+     */
+    public function withReason(string $reason): self
+    {
+        $validator = new \JsonSchema\Validator();
+        $validator->validate($reason, self::$internalValidationSchema['properties']['reason']);
+        if (!$validator->isValid()) {
+            throw new \InvalidArgumentException($validator->getErrors()[0]['message']);
+        }
+
+        $clone = clone $this;
+        $clone->reason = $reason;
+
+        return $clone;
+    }
+
+    /**
+     * @return array<string, string>
+     */
+    public function getAdditionalProperties(): array
+    {
+        return $this->additionalProperties;
+    }
+
+    /**
+     * @param array<string, string> $additionalProperties
+     * @return self
+     */
+    public function withAdditionalProperties(array $additionalProperties): self
+    {
+        $clone = clone $this;
+        $clone->additionalProperties = $additionalProperties;
+
+        return $clone;
+    }
+
+    /**
+     * Builds a new instance from an input array
+     *
+     * @param array|object $input Input data
+     * @param bool $validate Set this to false to skip validation; use at own risk
+     * @return Foo Created instance
+     * @throws \InvalidArgumentException
+     */
+    public static function buildFromInput(array|object $input, bool $validate = true): Foo
+    {
+        $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
+        if ($validate) {
+            static::validateInput($input);
+        }
+
+        $reason = $input->{'reason'};
+
+        $obj = new self($reason);
+
+        foreach (get_object_vars($input) as $key => $value) {
+            if (in_array($key, ['reason'], true)) {
+                continue;
+            }
+            $obj->additionalProperties[$key] = $value;
+        }
+        return $obj;
+    }
+
+    /**
+     * Converts this object back to a simple array that can be JSON-serialized
+     *
+     * @return array Converted array
+     */
+    public function toJson(): array
+    {
+        $output = [];
+        foreach ($this->additionalProperties as $key => $value) {
+            $output[$key] = $value;
+        }
+        $output['reason'] = $this->reason;
+
+        return $output;
+    }
+
+    /**
+     * Validates an input array
+     *
+     * @param array|object $input Input data
+     * @param bool $return Return instead of throwing errors
+     * @return bool Validation result
+     * @throws \InvalidArgumentException
+     */
+    public static function validateInput(array|object $input, bool $return = false): bool
+    {
+        $validator = new \JsonSchema\Validator();
+        $input = is_array($input) ? \JsonSchema\Validator::arrayToObjectRecursive($input) : $input;
+        $validator->validate($input, self::$internalValidationSchema);
+
+        if (!$validator->isValid() && !$return) {
+            $errors = array_map(function(array $e): string {
+                return $e["property"] . ": " . $e["message"];
+            }, $validator->getErrors());
+            throw new \InvalidArgumentException(join(", ", $errors));
+        }
+
+        return $validator->isValid();
+    }
+
+    public function __clone()
+    {
+    }
+}
\ No newline at end of file
diff --git a/tests/Generator/Fixtures/PropsWithAdditionalProps/schema.yaml b/tests/Generator/Fixtures/PropsWithAdditionalProps/schema.yaml
new file mode 100644
index 00000000..32231d1e
--- /dev/null
+++ b/tests/Generator/Fixtures/PropsWithAdditionalProps/schema.yaml
@@ -0,0 +1,8 @@
+type: object
+required:
+  - reason
+properties:
+  reason:
+    type: string
+additionalProperties:
+  type: string