diff --git a/mux.c b/mux.c
index 1cfb914..c8812a7 100644
--- a/mux.c
+++ b/mux.c
@@ -306,7 +306,7 @@ static int handle_receive_buf(struct ios_ops *ios, unsigned char *buf, int len)
 	unsigned char *sendbuf = buf;
 	int i;
 
-	while (len) {
+	while (len > 0) {
 		switch (*buf) {
 		case IAC:
 			/* BUG: this is telnet specific */