diff --git a/lib/Doctrine/ORM/Tools/SchemaTool.php b/lib/Doctrine/ORM/Tools/SchemaTool.php
index 2e9feb1f5..60760e66c 100644
--- a/lib/Doctrine/ORM/Tools/SchemaTool.php
+++ b/lib/Doctrine/ORM/Tools/SchemaTool.php
@@ -223,7 +223,7 @@ class SchemaTool
 
             if (isset($class->table['indexes'])) {
                 foreach ($class->table['indexes'] AS $indexName => $indexData) {
-                    $table->addIndex($indexData['columns'], $indexName);
+                    $table->addIndex($indexData['columns'], is_numeric($indexName) ? null : $indexName);
                 }
             }