diff --git a/sesman/tools/xcon.c b/sesman/tools/xcon.c
index 4150d6af..4b3248b6 100644
--- a/sesman/tools/xcon.c
+++ b/sesman/tools/xcon.c
@@ -19,6 +19,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 #include <sys/types.h>
 #include <X11/Xlib.h>