diff --git a/lightningd/channel/channel.c b/lightningd/channel/channel.c
index 0769a336d..93931f836 100644
--- a/lightningd/channel/channel.c
+++ b/lightningd/channel/channel.c
@@ -945,6 +945,9 @@ static void init_channel(struct peer *peer, const u8 *msg)
 		status_failed(WIRE_CHANNEL_BAD_COMMAND, "%s",
 			      tal_hex(msg, msg));
 
+	/* channel_id is set from funding txout */
+	derive_channel_id(&peer->channel_id, &funding_txid, funding_txout);
+
 	/* We derive everything from the one secret seed. */
 	derive_basepoints(&seed, &funding_pubkey[LOCAL], &points[LOCAL],
 			  &peer->our_secrets, &peer->shaseed,
diff --git a/lightningd/opening/opening.c b/lightningd/opening/opening.c
index 133ff9ae5..5f3c9f2c5 100644
--- a/lightningd/opening/opening.c
+++ b/lightningd/opening/opening.c
@@ -3,7 +3,6 @@
 #include <bitcoin/privkey.h>
 #include <bitcoin/script.h>
 #include <ccan/breakpoint/breakpoint.h>
-#include <ccan/build_assert/build_assert.h>
 #include <ccan/fdpass/fdpass.h>
 #include <ccan/structeq/structeq.h>
 #include <errno.h>
@@ -150,22 +149,6 @@ static void set_reserve(u64 *reserve, u64 funding)
 	*reserve = (funding + 99) / 100;
 }
 
-/* BOLT #2:
- *
- * This message introduces the `channel-id` which identifies , which is
- * derived from the funding transaction by combining the `funding-txid` and
- * the `funding-output-index` using big-endian exclusive-OR
- * (ie. `funding-output-index` alters the last two bytes).
- */
-static void derive_channel_id(struct channel_id *channel_id,
-			      struct sha256_double *txid, u16 txout)
-{
-	BUILD_ASSERT(sizeof(*channel_id) == sizeof(*txid));
-	memcpy(channel_id, txid, sizeof(*channel_id));
-	channel_id->id[sizeof(*channel_id)-2] ^= txout >> 8;
-	channel_id->id[sizeof(*channel_id)-1] ^= txout;
-}
-
 /* BOLT #2:
  *
  * A sending node MUST ensure `temporary-channel-id` is unique from any other
diff --git a/wire/fromwire.c b/wire/fromwire.c
index ef7ebf656..da7a4c2b7 100644
--- a/wire/fromwire.c
+++ b/wire/fromwire.c
@@ -3,6 +3,7 @@
 #include <bitcoin/preimage.h>
 #include <bitcoin/pubkey.h>
 #include <bitcoin/shadouble.h>
+#include <ccan/build_assert/build_assert.h>
 #include <ccan/endian/endian.h>
 #include <ccan/mem/mem.h>
 #include <ccan/tal/str/str.h>
@@ -178,3 +179,20 @@ static char *fmt_short_channel_id(const tal_t *ctx,
 }
 REGISTER_TYPE_TO_STRING(short_channel_id, fmt_short_channel_id);
 REGISTER_TYPE_TO_HEXSTR(channel_id);
+
+/* BOLT #2:
+ *
+ * This message introduces the `channel-id` which identifies , which is
+ * derived from the funding transaction by combining the `funding-txid` and
+ * the `funding-output-index` using big-endian exclusive-OR
+ * (ie. `funding-output-index` alters the last two bytes).
+ */
+void derive_channel_id(struct channel_id *channel_id,
+		       struct sha256_double *txid, u16 txout)
+{
+	BUILD_ASSERT(sizeof(*channel_id) == sizeof(*txid));
+	memcpy(channel_id, txid, sizeof(*channel_id));
+	channel_id->id[sizeof(*channel_id)-2] ^= txout >> 8;
+	channel_id->id[sizeof(*channel_id)-1] ^= txout;
+}
+
diff --git a/wire/wire.h b/wire/wire.h
index 2188334a6..ae93e607a 100644
--- a/wire/wire.h
+++ b/wire/wire.h
@@ -22,6 +22,9 @@ struct ipv6 {
 };
 struct preimage;
 
+void derive_channel_id(struct channel_id *channel_id,
+		       struct sha256_double *txid, u16 txout);
+
 /* Read the type; returns -1 if not long enough.  cursor is a tal ptr. */
 int fromwire_peektype(const u8 *cursor);