diff --git a/common/htlc_wire.c b/common/htlc_wire.c
index b50e7c291..49c8211de 100644
--- a/common/htlc_wire.c
+++ b/common/htlc_wire.c
@@ -78,6 +78,18 @@ struct existing_htlc *new_existing_htlc(const tal_t *ctx,
 	return existing;
 }
 
+static void towire_len_and_tlvstream(u8 **pptr, struct tlv_field *extra_tlvs)
+{
+	/* Making a copy is a bit awful, but it's the easiest way to
+	 * get the length */
+	u8 *tmp_pptr = tal_arr(tmpctx, u8, 0);
+	towire_tlvstream_raw(&tmp_pptr, extra_tlvs);
+
+	assert(tal_bytelen(tmp_pptr) == (u16)tal_bytelen(tmp_pptr));
+	towire_u16(pptr, tal_bytelen(tmp_pptr));
+	towire_u8_array(pptr, tmp_pptr, tal_bytelen(tmp_pptr));
+}
+
 /* FIXME: We could adapt tools/generate-wire.py to generate structures
  * and code like this. */
 void towire_added_htlc(u8 **pptr, const struct added_htlc *added)
@@ -94,13 +106,8 @@ void towire_added_htlc(u8 **pptr, const struct added_htlc *added)
 	} else
 		towire_bool(pptr, false);
 	if (added->extra_tlvs) {
-		u8 *tmp_pptr = tal_arr(tmpctx, u8, 0);
-		towire_tlvstream_raw(&tmp_pptr, added->extra_tlvs);
-
 		towire_bool(pptr, true);
-		towire_u16(pptr, tal_bytelen(tmp_pptr));
-		towire_u8_array(pptr, tmp_pptr,
-				tal_bytelen(tmp_pptr));
+		towire_len_and_tlvstream(pptr, added->extra_tlvs);
 	} else
 		towire_bool(pptr, false);
 	towire_bool(pptr, added->fail_immediate);
@@ -131,13 +138,8 @@ void towire_existing_htlc(u8 **pptr, const struct existing_htlc *existing)
 	} else
 		towire_bool(pptr, false);
 	if (existing->extra_tlvs) {
-		u8 *tmp_pptr = tal_arr(tmpctx, u8, 0);
-		towire_tlvstream_raw(&tmp_pptr, existing->extra_tlvs);
-
 		towire_bool(pptr, true);
-		towire_u16(pptr, tal_bytelen(tmp_pptr));
-		towire_u8_array(pptr, tmp_pptr,
-				tal_bytelen(tmp_pptr));
+		towire_len_and_tlvstream(pptr, existing->extra_tlvs);
 	} else
 		towire_bool(pptr, false);
 }
@@ -192,6 +194,28 @@ void towire_shachain(u8 **pptr, const struct shachain *shachain)
 	}
 }
 
+static struct tlv_field *fromwire_len_and_tlvstream(const tal_t *ctx,
+						    const u8 **cursor, size_t *max)
+{
+	struct tlv_field *tlvs = tal_arr(ctx, struct tlv_field, 0);
+	size_t len = fromwire_u16(cursor, max);
+
+	/* Subtle: we are not using fromwire_tal_arrn here, which
+	 * would do this. */
+	if (len > *max) {
+		fromwire_fail(cursor, max);
+		return NULL;
+	}
+
+	/* NOTE: We might consider to be more strict and only allow for
+	 * known tlv types from the tlvs_tlv_update_add_htlc_tlvs
+	 * record. */
+	if (!fromwire_tlv(cursor, &len, NULL, 0, cast_const(void *, ctx),
+			  &tlvs, FROMWIRE_TLV_ANY_TYPE, NULL, NULL))
+		return tal_free(tlvs);
+	return tlvs;
+}
+
 void fromwire_added_htlc(const u8 **cursor, size_t *max,
 			 struct added_htlc *added)
 {
@@ -207,17 +231,7 @@ void fromwire_added_htlc(const u8 **cursor, size_t *max,
 	} else
 		added->path_key = NULL;
 	if (fromwire_bool(cursor, max)) {
-		size_t tlv_len = fromwire_u16(cursor, max);
-		/* NOTE: We might consider to be more strict and only allow for
-		 * known tlv types from the tlvs_tlv_update_add_htlc_tlvs
-		 * record. */
-		const u64 *allowed = cast_const(u64 *, FROMWIRE_TLV_ANY_TYPE);
-		added->extra_tlvs = tal_arr(added, struct tlv_field, 0);
-		if (!fromwire_tlv(cursor, &tlv_len, NULL, 0, added,
-				  &added->extra_tlvs, allowed, NULL, NULL)) {
-			tal_free(added->extra_tlvs);
-			added->extra_tlvs = NULL;
-		}
+		added->extra_tlvs = fromwire_len_and_tlvstream(added, cursor, max);
 	} else
 		added->extra_tlvs = NULL;
 	added->fail_immediate = fromwire_bool(cursor, max);
@@ -250,17 +264,7 @@ struct existing_htlc *fromwire_existing_htlc(const tal_t *ctx,
 	} else
 		existing->path_key = NULL;
 	if (fromwire_bool(cursor, max)) {
-		size_t tlv_len = fromwire_u16(cursor, max);
-		/* NOTE: We might consider to be more strict and only allow for
-		 * known tlv types from the tlvs_tlv_update_add_htlc_tlvs
-		 * record. */
-		const u64 *allowed = cast_const(u64 *, FROMWIRE_TLV_ANY_TYPE);
-		existing->extra_tlvs = tal_arr(existing, struct tlv_field, 0);
-		if (!fromwire_tlv(cursor, &tlv_len, NULL, 0, existing,
-				  &existing->extra_tlvs, allowed, NULL, NULL)) {
-			tal_free(existing->extra_tlvs);
-			existing->extra_tlvs = NULL;
-		}
+		existing->extra_tlvs = fromwire_len_and_tlvstream(existing, cursor, max);
 	} else
 		existing->extra_tlvs = NULL;
 	return existing;