diff --git a/layout/base/nsPresShell.cpp b/layout/base/nsPresShell.cpp
index ecf4e741a274..1dbd93419312 100644
--- a/layout/base/nsPresShell.cpp
+++ b/layout/base/nsPresShell.cpp
@@ -1864,7 +1864,7 @@ nsresult PresShell::CreatePreferenceStyleSheet(void)
     result = NS_NewURI(getter_AddRefs(uri), "about:PreferenceStyleSheet", nsnull);
     if (NS_SUCCEEDED(result)) {
       NS_ASSERTION(uri, "null but no error");
-      result = mPrefStyleSheet->SetURIs(uri, nsnull, uri);
+      result = mPrefStyleSheet->SetURIs(uri, uri, uri);
       if (NS_SUCCEEDED(result)) {
         mPrefStyleSheet->SetComplete();
         PRUint32 index;