diff --git a/lib/Doctrine/ORM/Tools/SchemaValidator.php b/lib/Doctrine/ORM/Tools/SchemaValidator.php
index e98372d4c..f91bfff25 100644
--- a/lib/Doctrine/ORM/Tools/SchemaValidator.php
+++ b/lib/Doctrine/ORM/Tools/SchemaValidator.php
@@ -106,7 +106,7 @@ class SchemaValidator
 
             $targetMetadata = $cmf->getMetadataFor($assoc['targetEntity']);
 
-            if ($assoc['id'] && $targetMetadata->containsForeignIdentifier) {
+            if (isset($assoc['id']) && $targetMetadata->containsForeignIdentifier) {
                 $ce[] = "Cannot map association '" . $class->name. "#". $fieldName ." as identifier, because " .
                         "the target entity '". $targetMetadata->name . "' also maps an association as identifier.";
             }