diff --git a/toolbox/cmp.c b/toolbox/cmp.c
index 9bd2e19..80635ad 100644
--- a/toolbox/cmp.c
+++ b/toolbox/cmp.c
@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdint.h>
+#include <unistd.h>
 #include <fcntl.h>
 #include <sys/ioctl.h>
 #include <errno.h>