diff --git a/src/Symfony/Component/Serializer/Normalizer/ObjectNormalizer.php b/src/Symfony/Component/Serializer/Normalizer/ObjectNormalizer.php
index 88732bbd3e..f766286b2b 100644
--- a/src/Symfony/Component/Serializer/Normalizer/ObjectNormalizer.php
+++ b/src/Symfony/Component/Serializer/Normalizer/ObjectNormalizer.php
@@ -43,7 +43,10 @@ class ObjectNormalizer extends AbstractObjectNormalizer
         parent::__construct($classMetadataFactory, $nameConverter, $propertyTypeExtractor, $classDiscriminatorResolver, $objectClassResolver, $defaultContext);
 
         $this->propertyAccessor = $propertyAccessor ?: PropertyAccess::createPropertyAccessor();
-        $this->objectClassResolver = $objectClassResolver;
+
+        $this->objectClassResolver = $objectClassResolver ?? function ($class) {
+            return \is_object($class) ? \get_class($class) : $class;
+        };
     }
 
     /**
@@ -63,7 +66,7 @@ class ObjectNormalizer extends AbstractObjectNormalizer
         $attributes = [];
 
         // methods
-        $class = $this->objectClassResolver ? ($this->objectClassResolver)($object) : \get_class($object);
+        $class = ($this->objectClassResolver)($object);
         $reflClass = new \ReflectionClass($class);
 
         foreach ($reflClass->getMethods(\ReflectionMethod::IS_PUBLIC) as $reflMethod) {
diff --git a/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php b/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
index b85ec8b5e2..4c4448dfe4 100644
--- a/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
+++ b/src/Symfony/Component/Serializer/Tests/Normalizer/ObjectNormalizerTest.php
@@ -1043,6 +1043,30 @@ class ObjectNormalizerTest extends TestCase
         $this->assertArrayHasKey('foo-Symfony\Component\Serializer\Tests\Normalizer\ObjectDummy-json-bar', $normalizer->normalize(new ObjectDummy(), 'json', ['foo' => 'bar']));
     }
 
+    public function testDefaultObjectClassResolver()
+    {
+        $normalizer = new ObjectNormalizer();
+
+        $obj = new ObjectDummy();
+        $obj->setFoo('foo');
+        $obj->bar = 'bar';
+        $obj->setBaz(true);
+        $obj->setCamelCase('camelcase');
+        $obj->unwantedProperty = 'notwanted';
+
+        $this->assertEquals(
+            [
+                'foo' => 'foo',
+                'bar' => 'bar',
+                'baz' => true,
+                'fooBar' => 'foobar',
+                'camelCase' => 'camelcase',
+                'object' => null,
+            ],
+            $normalizer->normalize($obj, 'any')
+        );
+    }
+
     public function testObjectClassResolver()
     {
         $classResolver = function ($object) {