diff --git a/src/DeepClone/DeepClone.php b/src/DeepClone/DeepClone.php
index 65dd5f9a..63bf5392 100644
--- a/src/DeepClone/DeepClone.php
+++ b/src/DeepClone/DeepClone.php
@@ -684,7 +684,7 @@ private static function prepare($values, &$objectsPool, &$refsPool, &$objectsCou
                     // method of that name, so it is gated behind
                     // allow_named_closures, which both ends must enable.
                     if (!$allowNamedClosures) {
-                        throw new \ValueError('deepclone_to_array(): serializing a closure over the named callable "'.$r->name.'" requires enabling the allow_named_closures option');
+                        throw new \ValueError('deepclone_to_array(): serializing a closure over the named callable "'.$r->name.'" requires enabling the "allow_named_closures" option; do it only if you trust the input; alternatively, install the "deepclone" extension, which can reference callables declared in constant expressions');
                     }
                     if (null !== $allowedSet && !isset($allowedSet['closure'])) {
                         throw new \ValueError('deepclone_to_array(): class "Closure" is not allowed');
@@ -1655,7 +1655,11 @@ private static function resolveConstExprClosureScalar($value, ?array $allowedCla
         if (null === $found) {
             throw new \ValueError('deepclone_from_array(): Argument #1 ($data) malformed payload, const-expr-closure references unknown closure index '.$closureIndex);
         }
-        if ($line !== $foundLine = (new \ReflectionFunction($found))->getStartLine()) {
+        // Internal functions (e.g. a global strlen(...) reference) have no
+        // start line; getStartLine() returns false, which the extension encodes
+        // as 0. Normalize so such a reference does not look stale.
+        $foundLine = (new \ReflectionFunction($found))->getStartLine() ?: 0;
+        if ($line !== $foundLine) {
             throw new \ValueError('deepclone_from_array(): Argument #1 ($data) stale payload, const-expr-closure moved from line '.$line.' to line '.$foundLine);
         }
 
diff --git a/tests/DeepClone/DeepCloneTest.php b/tests/DeepClone/DeepCloneTest.php
index 44fccc7e..72e7dc55 100644
--- a/tests/DeepClone/DeepCloneTest.php
+++ b/tests/DeepClone/DeepCloneTest.php
@@ -584,7 +584,9 @@ public function testClosurePrivateMethodWireFormatAndRoundTrip()
     public function testToArrayNamedClosureRequiresOptIn()
     {
         $this->expectException(\ValueError::class);
-        $this->expectExceptionMessage('serializing a closure over the named callable "strlen" requires enabling the allow_named_closures option');
+        // Substring common to the polyfill and extension messages (the polyfill
+        // quotes the option name and appends an extension hint).
+        $this->expectExceptionMessage('serializing a closure over the named callable "strlen" requires enabling the');
         deepclone_to_array(\Closure::fromCallable('strlen'));
     }
 
@@ -2554,4 +2556,21 @@ public function testToArrayConstExprClosureFirstClassCallableUsesDeclarationSite
         $this->assertSame(ConstExprFccFixture::class, $d['prepared'][0]);
         $this->assertTrue(deepclone_from_array($d)());
     }
+
+    /**
+     * @requires PHP 8.5
+     */
+    public function testFromArrayConstExprClosureGlobalInternalFunction()
+    {
+        // The extension can reference a global internal function declared in an
+        // attribute (e.g. #[ConstExprAttr(strlen(...))]); such a reference has
+        // no start line and is encoded with line 0. The polyfill cannot produce
+        // these (no reflection hook), but must decode them: ReflectionFunction
+        // reports no start line for an internal function, so the line-0
+        // reference must not be treated as stale.
+        $payload = ['classes' => '', 'objectMeta' => 0, 'prepared' => [ConstExprGlobalFccFixture::class, '$p', 0, 0, 0], 'mask' => 1];
+
+        $r = deepclone_from_array($payload);
+        $this->assertSame(5, $r('hello'));
+    }
 }
diff --git a/tests/DeepClone/fixtures85.php b/tests/DeepClone/fixtures85.php
index 87320124..7f6bc805 100644
--- a/tests/DeepClone/fixtures85.php
+++ b/tests/DeepClone/fixtures85.php
@@ -148,3 +148,9 @@ public static function helper(): bool
         return true;
     }
 }
+
+class ConstExprGlobalFccFixture
+{
+    #[ConstExprAttr(strlen(...))]
+    public string $p = '';
+}