diff --git a/channeld/channel.c b/channeld/channel.c
index b4c061d34..42fb62d8f 100644
--- a/channeld/channel.c
+++ b/channeld/channel.c
@@ -1759,6 +1759,8 @@ static void handle_offer_htlc(struct peer *peer, const u8 *inmsg)
 	abort();
 
 failed:
+	/* Note: tal_fmt doesn't set tal_len() to exact length, so fix here. */
+	tal_resize(&failmsg, strlen(failmsg)+1);
 	msg = towire_channel_offer_htlc_reply(inmsg, 0, failcode, (u8*)failmsg);
 	daemon_conn_send(&peer->master, take(msg));
 }