diff --git a/cmd/sleep.c b/cmd/sleep.c
index 7616fed..a8c896e 100644
--- a/cmd/sleep.c
+++ b/cmd/sleep.c
@@ -9,6 +9,7 @@
 #include <time.h>
 #include <vsprintf.h>
 #include <linux/delay.h>
+#include <linux/string.h>
 
 static int do_sleep(struct cmd_tbl *cmdtp, int flag, int argc,
 		    char *const argv[])