diff --git a/gdk/win32/gdkgeometry-win32.c b/gdk/win32/gdkgeometry-win32.c
index fb2b363b1..6cdb860cc 100644
--- a/gdk/win32/gdkgeometry-win32.c
+++ b/gdk/win32/gdkgeometry-win32.c
@@ -196,7 +196,7 @@ void
 _gdk_win32_window_tmp_reset_bg (GdkWindow *window,
 				gboolean   recurse)
 {
-  GdkWindowObject *private;
+  GdkWindowObject *private = (GdkWindowObject*)window;
 
   g_return_if_fail (GDK_IS_WINDOW (window));