diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index c0f76da..c09db11 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2269,14 +2269,15 @@
 	char *f;
 	int i;
 	char buf[64];
-	char flags;
+	char flags = TTY_NORMAL;
 
 	if (debug & 4)
 		print_hex_dump_bytes("gsmld_receive: ", DUMP_PREFIX_OFFSET,
 				     cp, count);
 
 	for (i = count, dp = cp, f = fp; i; i--, dp++) {
-		flags = *f++;
+		if (f)
+			flags = *f++;
 		switch (flags) {
 		case TTY_NORMAL:
 			gsm->receive(gsm, *dp);