diff --git a/glib/gutils.h b/glib/gutils.h
index 95114d8e3..1dd5e56ae 100644
--- a/glib/gutils.h
+++ b/glib/gutils.h
@@ -304,7 +304,7 @@ g_bit_storage (gulong number)
 {
 #if defined(__GNUC__) && (__GNUC__ >= 4) && defined(__OPTIMIZE__)
   return G_LIKELY (number) ?
-	   ((GLIB_SIZEOF_LONG * 8U - 1) ^ __builtin_clzl(number)) + 1 : 1;
+	   ((GLIB_SIZEOF_LONG * 8U - 1) ^ (guint) __builtin_clzl(number)) + 1 : 1;
 #else
   register guint n_bits = 0;