diff --git a/gfx/src/gtk/nsRenderingContextGTK.cpp b/gfx/src/gtk/nsRenderingContextGTK.cpp
index 6c03ce186401..d00793f92f71 100644
--- a/gfx/src/gtk/nsRenderingContextGTK.cpp
+++ b/gfx/src/gtk/nsRenderingContextGTK.cpp
@@ -492,7 +492,7 @@ GdkGC *nsRenderingContextGTK::GetGC()
 void nsRenderingContextGTK::UpdateGC()
 {
   GdkGCValues values;
-  GdkGCValuesMask valuesMask;
+  unsigned int valuesMask;
 
   values.font = mCurrentFont;
   values.foreground.pixel = gdk_rgb_xpixel_from_rgb(NS_TO_GDK_RGB(mCurrentColor));
@@ -514,7 +514,7 @@ void nsRenderingContextGTK::UpdateGC()
 
   mGC = gcCache->GetClipGC(mSurface->GetDrawable(), 
                            &values,
-                           valuesMask,
+                           (GdkGCValuesMask)valuesMask,
                            rgn);