diff --git a/tools/gen/header_template b/tools/gen/header_template
index 56dbd3c1846a..2cd7ad50c55a 100644
--- a/tools/gen/header_template
+++ b/tools/gen/header_template
@@ -68,6 +68,18 @@ struct ${tlv.struct_name()} {
 struct ${tlv.struct_name()} *${tlv.struct_name()}_new(const tal_t *ctx);
 bool fromwire_${tlv.name}(const u8 **cursor, size_t *max, struct ${tlv.struct_name()} *record);
 
+/**
+ * Check that the TLV stream is valid.
+ *
+ * Enforces the followin validity rules:
+ * - Types must be in monotonic non-repeating order
+ * - We must understand all even types
+ *
+ * Returns the index of the field that was invalid, or -1 if the stream is
+ * valid.
+ */
+int ${tlv.name}_is_valid(const struct ${tlv.struct_name()} *record);
+
 % if tlv.name in options.expose_tlv_type:
 #define TLVS_${tlv.name.upper()}_ARRAY_SIZE ${len(tlv.messages)}
 extern const struct tlv_record_type tlvs_${tlv.name}[];
diff --git a/tools/gen/impl_template b/tools/gen/impl_template
index d559ea782bff..296328ce0f4e 100644
--- a/tools/gen/impl_template
+++ b/tools/gen/impl_template
@@ -304,6 +304,41 @@ fail:
 	fromwire_fail(cursor, max);
 	return false;
 }
+
+int ${tlv.name}_is_valid(const struct ${tlv.struct_name()} *record)
+{
+	size_t numfields = tal_count(record->fields);
+	bool first = true;
+	u64 prev_type = 0;
+	for (int i=0; i<numfields; i++) {
+		struct tlv_field *f = &record->fields[i];
+		if (f->numtype % 2 == 0 && f->meta == NULL) {
+			/* BOLT #1:
+			 * - otherwise, if `type` is unknown:
+			 *   - if `type` is even:
+			 *     - MUST fail to parse the `tlv_stream`.
+			 *   - otherwise, if `type` is odd:
+			 *     - MUST discard the next `length` bytes.
+			 */
+			SUPERVERBOSE("Unknown even type in TLV");
+			return i;
+		} else if (!first && f->numtype <= prev_type) {
+			/* BOLT #1:
+			 *  - if decoded `type`s are not monotonically-increasing:
+			 *    - MUST fail to parse the `tlv_stream`.
+			 */
+			if (f->numtype == prev_type)
+				SUPERVERBOSE("duplicate tlv type");
+			else
+				SUPERVERBOSE("invalid ordering");
+			return i;
+		}
+		first = false;
+		prev_type = f->numtype;
+	}
+	return -1;
+}
+
 % endfor ##  END TLV's
 % for msg in messages: ## START Wire Messages
 
diff --git a/wallet/test/run-wallet.c b/wallet/test/run-wallet.c
index c3e0ae6abfef..6854b38e2b80 100644
--- a/wallet/test/run-wallet.c
+++ b/wallet/test/run-wallet.c
@@ -554,6 +554,9 @@ void subd_req_(const tal_t *ctx UNNEEDED,
 /* Generated stub for subd_send_msg */
 void subd_send_msg(struct subd *sd UNNEEDED, const u8 *msg_out UNNEEDED)
 { fprintf(stderr, "subd_send_msg called!\n"); abort(); }
+/* Generated stub for tlv_payload_is_valid */
+int tlv_payload_is_valid(const struct tlv_tlv_payload *record UNNEEDED)
+{ fprintf(stderr, "tlv_payload_is_valid called!\n"); abort(); }
 /* Generated stub for topology_add_sync_waiter_ */
 void topology_add_sync_waiter_(const tal_t *ctx UNNEEDED,
 			       struct chain_topology *topo UNNEEDED,