diff --git a/shm.c b/shm.c
index 8a0a136d..751e265d 100644
--- a/shm.c
+++ b/shm.c
@@ -25,6 +25,10 @@
 #include "macros.h"
 #include "xmalloc.h"
 
+#if !defined(MAP_UNINITIALIZED)
+ #define MAP_UNINITIALIZED 0
+#endif
+
 #define TIME_SCROLL 0
 
 /*