--- a/io/mmap.c
+++ b/io/mmap.c
@@ -11,6 +11,10 @@
 #include "init.h"
 #include "io.h"
 
+#ifndef MAP_SYNC
+#define MAP_SYNC 0
+#endif
+
 static cmdinfo_t mmap_cmd;
 static cmdinfo_t mread_cmd;
 static cmdinfo_t msync_cmd;