diff --git a/src/Metadata/Driver/AnnotationDriver.php b/src/Metadata/Driver/AnnotationDriver.php
index 1a8cb0d07..a04d5591f 100644
--- a/src/Metadata/Driver/AnnotationDriver.php
+++ b/src/Metadata/Driver/AnnotationDriver.php
@@ -73,7 +73,10 @@ public function __construct(Reader $reader, PropertyNamingStrategyInterface $nam
     public function loadMetadataForClass(\ReflectionClass $class): ?BaseClassMetadata
     {
         $classMetadata = new ClassMetadata($name = $class->name);
-        $classMetadata->fileResources[] = $class->getFilename();
+        $fileResource =  $class->getFilename();
+        if (false !== $fileResource) {
+            $classMetadata->fileResources[] = $fileResource;
+        }
 
         $propertiesMetadata = [];
         $propertiesAnnotations = [];
diff --git a/src/Metadata/Driver/NullDriver.php b/src/Metadata/Driver/NullDriver.php
index 3d8057abb..fbbf750f0 100644
--- a/src/Metadata/Driver/NullDriver.php
+++ b/src/Metadata/Driver/NullDriver.php
@@ -13,7 +13,10 @@ class NullDriver implements DriverInterface
     public function loadMetadataForClass(\ReflectionClass $class): ?BaseClassMetadata
     {
         $classMetadata = new ClassMetadata($name = $class->name);
-        $classMetadata->fileResources[] = $class->getFilename();
+        $fileResource =  $class->getFilename();
+        if (false !== $fileResource) {
+            $classMetadata->fileResources[] = $fileResource;
+        }
 
         return $classMetadata;
     }
diff --git a/src/Metadata/Driver/XmlDriver.php b/src/Metadata/Driver/XmlDriver.php
index b2c0390c7..c894c9ccf 100644
--- a/src/Metadata/Driver/XmlDriver.php
+++ b/src/Metadata/Driver/XmlDriver.php
@@ -56,7 +56,10 @@ protected function loadMetadataFromFile(\ReflectionClass $class, string $path):
         $elem = reset($elems);
 
         $metadata->fileResources[] = $path;
-        $metadata->fileResources[] = $class->getFileName();
+        $fileResource =  $class->getFilename();
+        if (false !== $fileResource) {
+            $metadata->fileResources[] = $fileResource;
+        }
         $exclusionPolicy = strtoupper((string) $elem->attributes()->{'exclusion-policy'}) ?: 'NONE';
         $exclude = $elem->attributes()->exclude;
         $excludeAll = null !== $exclude ? 'true' === strtolower((string) $exclude) : false;
diff --git a/src/Metadata/Driver/YamlDriver.php b/src/Metadata/Driver/YamlDriver.php
index c083370c6..20b2e81a7 100644
--- a/src/Metadata/Driver/YamlDriver.php
+++ b/src/Metadata/Driver/YamlDriver.php
@@ -48,7 +48,11 @@ protected function loadMetadataFromFile(\ReflectionClass $class, string $file):
         $config = $config[$name];
         $metadata = new ClassMetadata($name);
         $metadata->fileResources[] = $file;
-        $metadata->fileResources[] = $class->getFileName();
+        $fileResource =  $class->getFilename();
+        if (false !== $fileResource) {
+            $metadata->fileResources[] = $fileResource;
+        }
+
         $exclusionPolicy = isset($config['exclusion_policy']) ? strtoupper($config['exclusion_policy']) : 'NONE';
         $excludeAll = isset($config['exclude']) ? (bool) $config['exclude'] : false;
         $classAccessType = $config['access_type'] ?? PropertyMetadata::ACCESS_TYPE_PROPERTY;
diff --git a/tests/Metadata/Driver/AnnotationDriverTest.php b/tests/Metadata/Driver/AnnotationDriverTest.php
index b9be6866f..8bba7acf7 100644
--- a/tests/Metadata/Driver/AnnotationDriverTest.php
+++ b/tests/Metadata/Driver/AnnotationDriverTest.php
@@ -14,4 +14,9 @@ protected function getDriver()
     {
         return new AnnotationDriver(new AnnotationReader(), new IdenticalPropertyNamingStrategy());
     }
+
+    public function testCanDefineMetadataForInternalClass()
+    {
+        $this->markTestSkipped('Can not define annotation metadata for internal classes');
+    }
 }
diff --git a/tests/Metadata/Driver/BaseDriverTest.php b/tests/Metadata/Driver/BaseDriverTest.php
index bf686a6ea..1516fae86 100644
--- a/tests/Metadata/Driver/BaseDriverTest.php
+++ b/tests/Metadata/Driver/BaseDriverTest.php
@@ -271,6 +271,17 @@ public function testLoadXmlDiscriminatorWithNamespaces()
         self::assertFalse($m->xmlDiscriminatorAttribute);
     }
 
+    public function testCanDefineMetadataForInternalClass()
+    {
+        /** @var ClassMetadata $m */
+        $m = $this->getDriver()->loadMetadataForClass(new \ReflectionClass(\PDOStatement::class));
+
+        self::assertNotNull($m);
+        self::assertSame('int', $m->propertyMetadata['queryString']->type['name']);
+
+        self::assertCount(1, $m->fileResources);
+    }
+
     public function testLoadXmlDiscriminatorWithAttributeNamespaces()
     {
         /** @var ClassMetadata $m */
diff --git a/tests/Metadata/Driver/XmlDriverTest.php b/tests/Metadata/Driver/XmlDriverTest.php
index b50193690..7a2802253 100644
--- a/tests/Metadata/Driver/XmlDriverTest.php
+++ b/tests/Metadata/Driver/XmlDriverTest.php
@@ -96,6 +96,7 @@ protected function getDriver()
 
         return new XmlDriver(new FileLocator([
             'JMS\Serializer\Tests\Fixtures' => __DIR__ . '/xml' . $append,
+            '' => __DIR__ . '/xml/_' . $append,
         ]), new IdenticalPropertyNamingStrategy());
     }
 }
diff --git a/tests/Metadata/Driver/YamlDriverTest.php b/tests/Metadata/Driver/YamlDriverTest.php
index 614eeb4a8..a2a48264d 100644
--- a/tests/Metadata/Driver/YamlDriverTest.php
+++ b/tests/Metadata/Driver/YamlDriverTest.php
@@ -76,6 +76,7 @@ private function getDriverForSubDir($subDir = null)
     {
         return new YamlDriver(new FileLocator([
             'JMS\Serializer\Tests\Fixtures' => __DIR__ . '/yml' . ($subDir ? '/' . $subDir : ''),
+            '' => __DIR__ . '/yml/_' . ($subDir ? '/' . $subDir : ''),
         ]), new IdenticalPropertyNamingStrategy());
     }
 
diff --git a/tests/Metadata/Driver/xml/_/PDOStatement.xml b/tests/Metadata/Driver/xml/_/PDOStatement.xml
new file mode 100644
index 000000000..63c13efb1
--- /dev/null
+++ b/tests/Metadata/Driver/xml/_/PDOStatement.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<serializer>
+    <class name="PDOStatement">
+        <property name="queryString" type="int"/>
+    </class>
+</serializer>
diff --git a/tests/Metadata/Driver/yml/_/PDOStatement.yml b/tests/Metadata/Driver/yml/_/PDOStatement.yml
new file mode 100644
index 000000000..9f2a91e14
--- /dev/null
+++ b/tests/Metadata/Driver/yml/_/PDOStatement.yml
@@ -0,0 +1,5 @@
+PDOStatement:
+    properties:
+        queryString:
+            type: int
+