diff --git a/glib/gutils.h b/glib/gutils.h
index bb4da8055..90281579c 100644
--- a/glib/gutils.h
+++ b/glib/gutils.h
@@ -355,7 +355,7 @@ g_bit_storage (gulong number)
 {
 #if defined(__GNUC__) && (__GNUC__ >= 4) && defined(__OPTIMIZE__)
   return G_LIKELY (number) ?
-	   ((GLIB_SIZEOF_LONG * 8 - 1) ^ __builtin_clzl(number)) + 1 : 1;
+	   ((GLIB_SIZEOF_LONG * 8U - 1) ^ __builtin_clzl(number)) + 1 : 1;
 #else
   register guint n_bits = 0;