diff --git a/wrt400n.c b/wrt400n.c
index a9a4908..f3c53db 100644
--- wrt400n.c
+++ wrt400n.c
@@ -11,6 +11,7 @@
 #include <stdio.h>
 #include <stdint.h>
 #include <string.h>
+#include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>