diff --git a/fs/fs.c b/fs/fs.c
index 79d432d..ea15c5f 100644
--- a/fs/fs.c
+++ b/fs/fs.c
@@ -276,6 +276,7 @@
 	unsigned long pos;
 	int len_read;
 	unsigned long time;
+	char *ep;
 
 	if (argc < 2)
 		return CMD_RET_USAGE;
@@ -286,7 +287,9 @@
 		return 1;
 
 	if (argc >= 4) {
-		addr = simple_strtoul(argv[3], NULL, 16);
+		addr = simple_strtoul(argv[3], &ep, 16);
+		if (ep == argv[3] || *ep != '\0')
+			return CMD_RET_USAGE;
 	} else {
 		addr_str = getenv("loadaddr");
 		if (addr_str != NULL)