diff --git a/toolkit/components/autocomplete/src/nsAutoCompleteController.cpp b/toolkit/components/autocomplete/src/nsAutoCompleteController.cpp
index 7687f55c8e05..e3510e95548f 100644
--- a/toolkit/components/autocomplete/src/nsAutoCompleteController.cpp
+++ b/toolkit/components/autocomplete/src/nsAutoCompleteController.cpp
@@ -819,7 +819,7 @@ nsAutoCompleteController::GetLevel(PRInt32 index, PRInt32 *_retval)
 NS_IMETHODIMP
 nsAutoCompleteController::GetParentIndex(PRInt32 rowIndex, PRInt32 *_retval)
 {
-  *_retval = 0;
+  *_retval = -1;
   return NS_OK;
 }