diff --git a/glib/gthread-posix.c b/glib/gthread-posix.c
index 9c0b032e6..1e2fdb59a 100644
--- a/glib/gthread-posix.c
+++ b/glib/gthread-posix.c
@@ -1177,7 +1177,7 @@ g_system_thread_new (GThreadFunc   proxy,
 #ifdef _SC_THREAD_STACK_MIN
       long min_stack_size = sysconf (_SC_THREAD_STACK_MIN);
       if (min_stack_size >= 0)
-        stack_size = MAX (min_stack_size, stack_size);
+        stack_size = MAX ((gulong) min_stack_size, stack_size);
 #endif /* _SC_THREAD_STACK_MIN */
       /* No error check here, because some systems can't do it and
        * we simply don't want threads to fail because of that. */