diff --git a/src/cairo-mutex-private.h b/src/cairo-mutex-private.h
index 5150b8ea9..ad0a94173 100644
--- a/src/cairo-mutex-private.h
+++ b/src/cairo-mutex-private.h
@@ -134,10 +134,12 @@ typedef int cairo_mutex_t;
 
 #else /**********************************************************************/
 
-# define CAIRO_MUTEX_LOCK(name)
-# define CAIRO_MUTEX_UNLOCK(name)
+# warning "XXX: No mutex implementation found.  Define CAIRO_NO_MUTEX to 1" \
+          "     to compile cairo without thread-safety support."
+
+#endif
+
 
-#endif  /********************************************************************/
 
 #ifndef CAIRO_MUTEX_DECLARE
 #define CAIRO_MUTEX_DECLARE(name) extern cairo_mutex_t name;