diff --git a/lib/Doctrine/ORM/Tools/SchemaTool.php b/lib/Doctrine/ORM/Tools/SchemaTool.php
index 3ab6139ef..ef27f2ed2 100644
--- a/lib/Doctrine/ORM/Tools/SchemaTool.php
+++ b/lib/Doctrine/ORM/Tools/SchemaTool.php
@@ -368,7 +368,7 @@ class SchemaTool
                     $constraint1['local'][] = $column['name'];
                     $constraint1['foreign'][] = $joinColumn['referencedColumnName'];
 
-                    if($joinColumn['unique'] == true) {
+                    if(isset($joinColumn['unique']) && $joinColumn['unique'] == true) {
                         $joinTableOptions['uniqueConstraints'][] = array($joinColumn['name']);
                     }