$OpenBSD$
--- src/zm_monitor.cpp.orig	Wed Feb  3 19:30:55 2016
+++ src/zm_monitor.cpp	Sat Apr  9 09:50:13 2016
@@ -51,6 +51,7 @@
 #include <sys/mman.h>
 #include <fcntl.h>
 #else // ZM_MEM_MAPPED
+#include <unistd.h>
 #include <sys/ipc.h>
 #include <sys/shm.h>
 #endif // ZM_MEM_MAPPED
