diff --git a/glib/gthread.h b/glib/gthread.h
index c8761c5e6..375771ad4 100644
--- a/glib/gthread.h
+++ b/glib/gthread.h
@@ -247,7 +247,7 @@ void            g_once_init_leave               (volatile void  *location,
 # define g_once_init_enter(location) \
   (G_GNUC_EXTENSION ({                                               \
     G_STATIC_ASSERT (sizeof *(location) == sizeof (gpointer));       \
-    (void) (0 ? (gpointer) *(location) : 0);                         \
+    (void) (0 ? (gpointer) *(location) : NULL);                      \
     (!g_atomic_pointer_get (location) &&                             \
      g_once_init_enter (location));                                  \
   }))