diff --git a/wire/Makefile b/wire/Makefile
index 03dc754d4..7d20f8214 100644
--- a/wire/Makefile
+++ b/wire/Makefile
@@ -5,17 +5,22 @@ wire-wrongdir:
 	$(MAKE) -C .. wire-all
 
 WIRE_HEADERS := wire/wire.h
-WIRE_GEN_HEADERS := wire/gen_peer_wire.h
+WIRE_GEN_HEADERS := wire/gen_peer_wire.h wire/gen_onion_wire.h
 WIRE_GEN_SRC := wire/gen_peer_wire.c
+WIRE_GEN_ONION_SRC := wire/gen_onion_wire.c
 WIRE_SRC := wire/fromwire.c	\
 		wire/towire.c
 
 WIRE_OBJS := $(WIRE_SRC:.c=.o) $(WIRE_GEN_SRC:.c=.o)
+WIRE_ONION_OBJS := $(WIRE_GEN_ONION_SRC:.c=.o)
 
 # They may not have the bolts.
 BOLT_EXTRACT=$(BOLTDIR)/tools/extract-formats.py
 wire/gen_peer_wire_csv: FORCE
-	@set -e; if [ -f $(BOLT_EXTRACT) ]; then for f in $(BOLTDIR)/*.md $(BOLT_EXTRACT); do if [ $$f -nt $@ -o ! -f $@ ]; then $(BOLT_EXTRACT) --message-fields --message-types --check-alignment $(BOLTDIR)/*.md > $@; break; fi; done; fi
+	@set -e; if [ -f $(BOLT_EXTRACT) ]; then for f in $(BOLTDIR)/0[127]*.md $(BOLT_EXTRACT); do if [ $$f -nt $@ -o ! -f $@ ]; then $(BOLT_EXTRACT) --message-fields --message-types --check-alignment $(BOLTDIR)/0[127]*.md > $@; break; fi; done; fi
+
+wire/gen_onion_wire_csv: FORCE
+	@set -e; if [ -f $(BOLT_EXTRACT) ]; then for f in $(BOLTDIR)/04*.md $(BOLT_EXTRACT); do if [ $$f -nt $@ -o ! -f $@ ]; then echo '#include <wire/onion_defs.h>' > $@ && $(BOLT_EXTRACT) --message-fields --message-types --check-alignment $(BOLTDIR)/04*.md >> $@; break; fi; done; fi
 
 wire/gen_peer_wire.h: $(WIRE_GEN) wire/gen_peer_wire_csv
 	$(WIRE_GEN) --header $@ wire_type < wire/gen_peer_wire_csv > $@
@@ -23,7 +28,14 @@ wire/gen_peer_wire.h: $(WIRE_GEN) wire/gen_peer_wire_csv
 wire/gen_peer_wire.c: $(WIRE_GEN) wire/gen_peer_wire_csv
 	$(WIRE_GEN) ${@:.c=.h} wire_type < wire/gen_peer_wire_csv > $@
 
+wire/gen_onion_wire.h: $(WIRE_GEN) wire/gen_onion_wire_csv
+	$(WIRE_GEN) --header $@ onion_type < wire/gen_onion_wire_csv > $@
+
+wire/gen_onion_wire.c: $(WIRE_GEN) wire/gen_onion_wire_csv
+	$(WIRE_GEN) ${@:.c=.h} onion_type < wire/gen_onion_wire_csv > $@
+
 wire/gen_peer_wire.o: wire/gen_peer_wire.h
+wire/gen_onion_wire.o: wire/gen_onion_wire.h
 
 check-source: $(WIRE_SRC:%=check-src-include-order/%) $(WIRE_HEADERS:%=check-hdr-include-order/%)
 
@@ -33,7 +45,7 @@ check-whitespace: $(WIRE_SRC:%=check-whitespace/%) $(WIRE_HEADERS:%=check-whites
 
 clean: wire-clean
 
-wire-all: wire/gen_peer_wire.o wire/fromwire.o wire/towire.o
+wire-all: wire/gen_peer_wire.o wire/gen_onion_wire.o wire/fromwire.o wire/towire.o
 
 wire-clean:
 	$(RM) $(WIRE_OBJS) $(WIRE_GEN_SRC) $(WIRE_GEN_HEADERS) towire.c fromwire.c
diff --git a/wire/gen_onion_wire_csv b/wire/gen_onion_wire_csv
new file mode 100644
index 000000000..7758ffceb
--- /dev/null
+++ b/wire/gen_onion_wire_csv
@@ -0,0 +1,29 @@
+#include <wire/onion_defs.h>
+invalid_realm,PERM|1
+temporary_node_failure,NODE|2
+permanent_node_failure,PERM|NODE|2
+required_node_feature_missing,PERM|NODE|3
+invalid_onion_version,BADONION|PERM|4
+invalid_onion_version,0,sha256-of-onion,32
+invalid_onion_hmac,BADONION|PERM|5
+invalid_onion_hmac,0,sha256-of-onion,32
+invalid_onion_key,BADONION|PERM|6
+invalid_onion_key,0,sha256-of-onion,32
+temporary_channel_failure,7
+permanent_channel_failure,PERM|8
+required_channel_feature_missing,PERM|9
+unknown_next_peer,PERM|10
+amount_below_minimum,UPDATE|11
+amount_below_minimum,0,htlc-msat,4
+amount_below_minimum,4,len,2
+fee_insufficient,UPDATE|12
+fee_insufficient,0,htlc-msat,4
+fee_insufficient,4,len,2
+incorrect_cltv_expiry,UPDATE|13
+incorrect_cltv_expiry,0,cltv-expiry,4
+incorrect_cltv_expiry,4,len,2
+expiry_too_soon,UPDATE|14
+expiry_too_soon,0,len,2
+unknown_payment_hash,PERM|15
+incorrect_payment_amount,PERM|16
+final_expiry_too_soon,17
diff --git a/wire/onion_defs.h b/wire/onion_defs.h
new file mode 100644
index 000000000..2902e8714
--- /dev/null
+++ b/wire/onion_defs.h
@@ -0,0 +1,18 @@
+/* Macro definitions for constants used in BOLT #4 */
+#ifndef LIGHTNING_WIRE_ONION_DEFS_H
+#define LIGHTNING_WIRE_ONION_DEFS_H
+
+/* BOLT #4:
+ *
+ * The top byte of `failure-code` can be read as a set of flags:
+ * * 0x8000 (BADONION): unparsable onion, encrypted by previous node.
+ * * 0x4000 (PERM): permanent failure (otherwise transient)
+ * * 0x2000 (NODE): node failure (otherwise channel)
+ * * 0x1000 (UPDATE): new channel update enclosed
+ */
+#define BADONION	0x8000
+#define PERM		0x4000
+#define NODE		0x2000
+#define UPDATE		0x1000
+
+#endif /* LIGHTNING_WIRE_ONION_DEFS_H */