diff --git a/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php b/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php
index a151c8703dd36..55add2f94b06c 100644
--- a/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php
+++ b/src/Symfony/Bridge/Doctrine/Validator/Constraints/UniqueEntityValidator.php
@@ -104,7 +104,7 @@ public function validate($entity, Constraint $constraint)
 
             $criteria[$fieldName] = $fieldValue;
 
-            if (null !== $criteria[$fieldName] && $class->hasAssociation($fieldName)) {
+            if (\is_object($criteria[$fieldName]) && $class->hasAssociation($fieldName)) {
                 /* Ensure the Proxy is initialized before using reflection to
                  * read its identifiers. This is necessary because the wrapped
                  * getter methods in the Proxy are being bypassed.