diff --git a/lib/Doctrine/ORM/Query/ResultSetMappingBuilder.php b/lib/Doctrine/ORM/Query/ResultSetMappingBuilder.php
index 6fc5b0611..804a208ef 100644
--- a/lib/Doctrine/ORM/Query/ResultSetMappingBuilder.php
+++ b/lib/Doctrine/ORM/Query/ResultSetMappingBuilder.php
@@ -438,8 +438,8 @@ class ResultSetMappingBuilder extends ResultSetMapping
                 $sql  .= $class->fieldMappings[$this->fieldMappings[$columnName]]['columnName'];
             } else if (isset($this->metaMappings[$columnName])) {
                 $sql .= $this->metaMappings[$columnName];
-            } else if (isset($this->discriminatorColumns[$columnName])) {
-                $sql .= $this->discriminatorColumns[$columnName];
+            } else if (isset($this->discriminatorColumns[$dqlAlias])) {
+                $sql .= $this->discriminatorColumns[$dqlAlias];
             }
 
             $sql .= " AS " . $columnName;