diff --git a/iscsi-scst/usr/chap.c b/iscsi-scst/usr/chap.c
index 227a372dc..fc709de21 100644
--- a/iscsi-scst/usr/chap.c
+++ b/iscsi-scst/usr/chap.c
@@ -29,6 +29,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <fcntl.h>
+#include <unistd.h>
 #include "sha1.h"
 #include "md5.h"