diff --git a/tools/generate-wire.py b/tools/generate-wire.py
index 2d7cbbec1..7c5a36656 100755
--- a/tools/generate-wire.py
+++ b/tools/generate-wire.py
@@ -14,6 +14,7 @@ type2size = {
     'struct short_channel_id': 8,
     'struct ipv6': 16,
     'secp256k1_ecdsa_signature': 64,
+    'struct preimage': 32,
     'struct pubkey': 33,
     'struct sha256': 32,
     'u64': 8,
@@ -57,6 +58,7 @@ typemap = {
     ('update_fail_htlc', 'reason'): FieldType('u8'),
     ('node_announcement', 'alias'): FieldType('u8'),
     ('update_add_htlc', 'onion_routing_packet'): FieldType('u8'),
+    ('update_fulfill_htlc', 'payment_preimage'): FieldType('struct preimage'),
     ('error', 'data'): FieldType('u8'),
     ('shutdown', 'scriptpubkey'): FieldType('u8'),
     ('node_announcement', 'rgb_color'): FieldType('u8'),
diff --git a/wire/fromwire.c b/wire/fromwire.c
index 3859525fa..ef7ebf656 100644
--- a/wire/fromwire.c
+++ b/wire/fromwire.c
@@ -1,5 +1,6 @@
 #include "utils.h"
 #include "wire.h"
+#include <bitcoin/preimage.h>
 #include <bitcoin/pubkey.h>
 #include <bitcoin/shadouble.h>
 #include <ccan/endian/endian.h>
@@ -150,6 +151,11 @@ void fromwire_sha256_double(const u8 **cursor, size_t *max,
 	fromwire_sha256(cursor, max, &sha256d->sha);
 }
 
+void fromwire_preimage(const u8 **cursor, size_t *max, struct preimage *preimage)
+{
+	fromwire(cursor, max, preimage, sizeof(*preimage));
+}
+
 void fromwire_ipv6(const u8 **cursor, size_t *max, struct ipv6 *ipv6)
 {
 	fromwire(cursor, max, ipv6, sizeof(*ipv6));
diff --git a/wire/test/run-peer-wire.c b/wire/test/run-peer-wire.c
index c8f7d3eda..3f22701f9 100644
--- a/wire/test/run-peer-wire.c
+++ b/wire/test/run-peer-wire.c
@@ -112,7 +112,7 @@ struct msg_accept_channel {
 struct msg_update_fulfill_htlc {
 	struct channel_id channel_id;
 	u64 id;
-	struct sha256 payment_preimage;
+	struct preimage payment_preimage;
 };
 struct msg_shutdown {
 	struct channel_id channel_id;
diff --git a/wire/towire.c b/wire/towire.c
index 3ec232cda..45b63e5a3 100644
--- a/wire/towire.c
+++ b/wire/towire.c
@@ -1,5 +1,6 @@
 #include "utils.h"
 #include "wire.h"
+#include <bitcoin/preimage.h>
 #include <bitcoin/shadouble.h>
 #include <ccan/endian/endian.h>
 #include <ccan/mem/mem.h>
@@ -94,6 +95,11 @@ void towire_sha256_double(u8 **pptr, const struct sha256_double *sha256d)
 	towire_sha256(pptr, &sha256d->sha);
 }
 
+void towire_preimage(u8 **pptr, const struct preimage *preimage)
+{
+	towire(pptr, preimage, sizeof(*preimage));
+}
+
 void towire_ipv6(u8 **pptr, const struct ipv6 *ipv6)
 {
 	towire(pptr, ipv6, sizeof(*ipv6));
diff --git a/wire/wire.h b/wire/wire.h
index 86639f82b..2188334a6 100644
--- a/wire/wire.h
+++ b/wire/wire.h
@@ -20,6 +20,7 @@ struct channel_id {
 struct ipv6 {
 	u8 addr[16];
 };
+struct preimage;
 
 /* Read the type; returns -1 if not long enough.  cursor is a tal ptr. */
 int fromwire_peektype(const u8 *cursor);
@@ -34,6 +35,7 @@ void towire_short_channel_id(u8 **pptr,
 			     const struct short_channel_id *short_channel_id);
 void towire_sha256(u8 **pptr, const struct sha256 *sha256);
 void towire_sha256_double(u8 **pptr, const struct sha256_double *sha256d);
+void towire_preimage(u8 **pptr, const struct preimage *preimage);
 void towire_ipv6(u8 **pptr, const struct ipv6 *ipv6);
 void towire_u8(u8 **pptr, u8 v);
 void towire_u16(u8 **pptr, u16 v);
@@ -61,6 +63,7 @@ void fromwire_short_channel_id(const u8 **cursor, size_t *max,
 void fromwire_sha256(const u8 **cursor, size_t *max, struct sha256 *sha256);
 void fromwire_sha256_double(const u8 **cursor, size_t *max,
 			    struct sha256_double *sha256d);
+void fromwire_preimage(const u8 **cursor, size_t *max, struct preimage *preimage);
 void fromwire_ipv6(const u8 **cursor, size_t *max, struct ipv6 *ipv6);
 void fromwire_pad(const u8 **cursor, size_t *max, size_t num);