diff --git a/channeld/channel.c b/channeld/channel.c
index 1851c28b8..902fc35e2 100644
--- a/channeld/channel.c
+++ b/channeld/channel.c
@@ -1214,7 +1214,7 @@ static u8 *got_commitsig_msg(const tal_t *ctx,
 				f = tal_arr_append(&failed);
 				*f = tal(failed, struct failed_htlc);
 				(*f)->id = htlc->id;
-				(*f)->malformed = htlc->failcode;
+				(*f)->failcode = htlc->failcode;
 				(*f)->failreason = cast_const(u8 *, htlc->fail);
 			}
 		} else {
diff --git a/channeld/full_channel.c b/channeld/full_channel.c
index b93a2a80f..ad85d5c94 100644
--- a/channeld/full_channel.c
+++ b/channeld/full_channel.c
@@ -1048,13 +1048,14 @@ bool channel_force_htlcs(struct channel *channel,
 				     htlc_state_name(htlc->state));
 			return false;
 		}
-		if (failed[i]->malformed)
-			htlc->failcode = failed[i]->malformed;
-		else
+		htlc->failcode = failed[i]->failcode;
+		if (failed[i]->failreason)
 			htlc->fail = tal_dup_arr(htlc, u8,
 						 failed[i]->failreason,
 						 tal_len(failed[i]->failreason),
 						 0);
+		else
+			htlc->fail = NULL;
 	}
 
 	for (i = 0; i < tal_count(htlcs); i++) {
diff --git a/common/htlc_wire.c b/common/htlc_wire.c
index 52d6dfaab..796465f1b 100644
--- a/common/htlc_wire.c
+++ b/common/htlc_wire.c
@@ -25,8 +25,11 @@ void towire_fulfilled_htlc(u8 **pptr, const struct fulfilled_htlc *fulfilled)
 
 void towire_failed_htlc(u8 **pptr, const struct failed_htlc *failed)
 {
+	/* Only one can be set. */
+	assert(failed->failcode || tal_len(failed->failreason));
+	assert(!failed->failcode || !tal_len(failed->failreason));
 	towire_u64(pptr, failed->id);
-	towire_u16(pptr, failed->malformed);
+	towire_u16(pptr, failed->failcode);
 	towire_u16(pptr, tal_count(failed->failreason));
 	towire_u8_array(pptr, failed->failreason, tal_count(failed->failreason));
 }
@@ -84,9 +87,12 @@ struct failed_htlc *fromwire_failed_htlc(const tal_t *ctx, const u8 **cursor, si
 	struct failed_htlc *failed = tal(ctx, struct failed_htlc);
 
 	failed->id = fromwire_u64(cursor, max);
-	failed->malformed = fromwire_u16(cursor, max);
+	failed->failcode = fromwire_u16(cursor, max);
 	failreason_len = fromwire_u16(cursor, max);
-	failed->failreason = tal_arr(failed, u8, failreason_len);
+	if (failreason_len)
+		failed->failreason = tal_arr(failed, u8, failreason_len);
+	else
+		failed->failreason = NULL;
 	fromwire_u8_array(cursor, max, failed->failreason, failreason_len);
 
 	return failed;
diff --git a/common/htlc_wire.h b/common/htlc_wire.h
index 8be698d14..3d0d76a62 100644
--- a/common/htlc_wire.h
+++ b/common/htlc_wire.h
@@ -26,7 +26,8 @@ struct fulfilled_htlc {
 
 struct failed_htlc {
 	u64 id;
-	enum onion_type malformed;
+	/* Either this is 0 and failreason non-NULL, or vice versa. */
+	enum onion_type failcode;
 	u8 *failreason;
 };
 
diff --git a/lightningd/peer_htlcs.c b/lightningd/peer_htlcs.c
index 888eed31e..8914dc756 100644
--- a/lightningd/peer_htlcs.c
+++ b/lightningd/peer_htlcs.c
@@ -771,8 +771,8 @@ static bool peer_failed_our_htlc(struct channel *channel,
 	if (!htlc_out_update_state(channel, hout, RCVD_REMOVE_COMMIT))
 		return false;
 
-	hout->failcode = failed->malformed;
-	if (!failed->malformed)
+	hout->failcode = failed->failcode;
+	if (!failed->failcode)
 		hout->failuremsg = tal_dup_arr(hout, u8, failed->failreason,
 					       tal_len(failed->failreason), 0);
 
@@ -1384,7 +1384,7 @@ static void add_fulfill(u64 id, enum side side,
 }
 
 static void add_fail(u64 id, enum side side,
-		     enum onion_type malformed,
+		     enum onion_type failcode,
 		     const u8 *failuremsg,
 		     const struct failed_htlc ***failed_htlcs,
 		     enum side **failed_sides)
@@ -1397,7 +1397,7 @@ static void add_fail(u64 id, enum side side,
 
 	*f = tal(*failed_htlcs, struct failed_htlc);
 	(*f)->id = id;
-	(*f)->malformed = malformed;
+	(*f)->failcode = failcode;
 	if (failuremsg)
 		(*f)->failreason
 			= tal_dup_arr(*f, u8, failuremsg, tal_len(failuremsg), 0);