diff --git a/content/xul/document/src/nsXULDocument.h b/content/xul/document/src/nsXULDocument.h
index 2ae7051cc650..7b146f24889b 100644
--- a/content/xul/document/src/nsXULDocument.h
+++ b/content/xul/document/src/nsXULDocument.h
@@ -420,7 +420,7 @@ protected:
     RemoveElementFromMap(nsIContent* aElement);
 
     static PRIntn
-    RemoveElementsFromMapByContent(const nsString& aID,
+    RemoveElementsFromMapByContent(const PRUnichar* aID,
                                    nsIContent* aElement,
                                    void* aClosure);
 
diff --git a/rdf/content/src/nsXULDocument.h b/rdf/content/src/nsXULDocument.h
index 2ae7051cc650..7b146f24889b 100644
--- a/rdf/content/src/nsXULDocument.h
+++ b/rdf/content/src/nsXULDocument.h
@@ -420,7 +420,7 @@ protected:
     RemoveElementFromMap(nsIContent* aElement);
 
     static PRIntn
-    RemoveElementsFromMapByContent(const nsString& aID,
+    RemoveElementsFromMapByContent(const PRUnichar* aID,
                                    nsIContent* aElement,
                                    void* aClosure);