diff --git a/content/base/src/nsDocument.cpp b/content/base/src/nsDocument.cpp
index 4567ccb8351..ad3d4fb2c19 100644
--- a/content/base/src/nsDocument.cpp
+++ b/content/base/src/nsDocument.cpp
@@ -1738,6 +1738,8 @@ nsDocument::GetElementsByClassNameHelper(nsINode* aRootNode,
     elements = new nsContentList(aRootNode, MatchClassNames,
                                  DestroyClassNameArray, classes);
   } else {
+    delete classes;
+    classes = nsnull;
     elements = new nsBaseContentList();
   }
   if (!elements) {