diff --git a/src/core/ArrayObject.php b/src/core/ArrayObject.php
index 19680f11..ccc0abce 100644
--- a/src/core/ArrayObject.php
+++ b/src/core/ArrayObject.php
@@ -651,6 +651,17 @@ public function usort(callable $value_compare_func): self
         return $this;
     }
 
+    public function isAssoc(): bool
+    {
+        foreach (array_keys($this->array) as $key) {
+            if (is_string($key)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /**
      * @param mixed $value
      * @return ArrayObject|mixed|StringObject
diff --git a/tests/unit/ArrayObjectTest.php b/tests/unit/ArrayObjectTest.php
index 68a9bea6..ed5848e1 100644
--- a/tests/unit/ArrayObjectTest.php
+++ b/tests/unit/ArrayObjectTest.php
@@ -581,4 +581,12 @@ public function testLastKey()
     {
         $this->assertEquals($this->data_4->lastKey(), 'c');
     }
+
+    public function testIsAssoc()
+    {
+        $this->assertFalse($this->data->isAssoc());
+        $this->assertFalse($this->data_2->isAssoc());
+        $this->assertTrue($this->data_3->isAssoc());
+        $this->assertTrue($this->data_4->isAssoc());
+    }
 }