--- a/widget/windows/nsLookAndFeel.cpp
+++ b/widget/windows/nsLookAndFeel.cpp
@@ -297,17 +297,19 @@ nsLookAndFeel::NativeGetColor(ColorID aI
       break;
     case eColorID__moz_buttondefault:
       idx = COLOR_3DDKSHADOW;
       break;
     case eColorID__moz_nativehyperlinktext:
       idx = COLOR_HOTLIGHT;
       break;
     default:
+      NS_WARNING("Unknown color for nsLookAndFeel");
       idx = COLOR_WINDOW;
+      res = NS_ERROR_FAILURE;
       break;
     }
 
   DWORD color = ::GetSysColor(idx);
   aColor = COLOREF_2_NSRGB(color);
 
   return res;
 }