diff --git a/lib/Doctrine/ORM/Tools/SchemaTool.php b/lib/Doctrine/ORM/Tools/SchemaTool.php
index 60760e66c..b0d14eb26 100644
--- a/lib/Doctrine/ORM/Tools/SchemaTool.php
+++ b/lib/Doctrine/ORM/Tools/SchemaTool.php
@@ -229,7 +229,7 @@ class SchemaTool
 
             if (isset($class->table['uniqueConstraints'])) {
                 foreach ($class->table['uniqueConstraints'] AS $indexName => $indexData) {
-                    $table->addUniqueIndex($indexData['columns'], $indexName);
+                    $table->addUniqueIndex($indexData['columns'], is_numeric($indexName) ? null : $indexName);
                 }
             }