diff --git a/lightningd/channel.c b/lightningd/channel.c
index ccf6430e6..5f37aebc9 100644
--- a/lightningd/channel.c
+++ b/lightningd/channel.c
@@ -733,6 +733,28 @@ bool channel_sending_revoke_and_ack(struct channel *channel)
 	return change & HTLC_REMOTE_F_PENDING;
 }
 
+/* FIXME: Trivial to optimize: set flag on channel_sending_commit,
+ * clear in channel_rcvd_revoke_and_ack. */
+bool channel_awaiting_revoke_and_ack(const struct channel *channel)
+{
+	const enum htlc_state states[] = { SENT_ADD_COMMIT,
+					   SENT_REMOVE_ACK_COMMIT,
+					   SENT_ADD_ACK_COMMIT,
+					   SENT_REMOVE_COMMIT };
+	struct htlc_map_iter it;
+	struct htlc *h;
+	size_t i;
+
+	for (h = htlc_map_first(&channel->htlcs, &it);
+	     h;
+	     h = htlc_map_next(&channel->htlcs, &it)) {
+		for (i = 0; i < ARRAY_SIZE(states); i++)
+			if (h->state == states[i])
+				return true;
+	}
+	return false;
+}
+
 static char *fmt_channel_view(const tal_t *ctx, const struct channel_view *view)
 {
 	return tal_fmt(ctx, "{ feerate_per_kw=%"PRIu64","
diff --git a/lightningd/channel.h b/lightningd/channel.h
index 16a49accc..82d38b3df 100644
--- a/lightningd/channel.h
+++ b/lightningd/channel.h
@@ -389,4 +389,11 @@ bool channel_rcvd_commit_(struct channel *channel,
  * anything changed for the remote commitment (ie. send a new commit).*/
 bool channel_sending_revoke_and_ack(struct channel *channel);
 
+/**
+ * channel_awaiting_revoke_and_ack: are we waiting for revoke_and_ack?
+ * @channel: the channel
+ *
+ * If true, we can't send a new commit message.
+ */
+bool channel_awaiting_revoke_and_ack(const struct channel *channel);
 #endif /* LIGHTNING_DAEMON_CHANNEL_H */
diff --git a/lightningd/channel/channel.c b/lightningd/channel/channel.c
index e7d927730..4f5911181 100644
--- a/lightningd/channel/channel.c
+++ b/lightningd/channel/channel.c
@@ -275,6 +275,13 @@ static void send_commit(struct peer *peer)
 	/* Timer has expired. */
 	peer->commit_timer = NULL;
 
+	/* FIXME: Document this requirement in BOLT 2! */
+	/* We can't send two commits in a row. */
+	if (channel_awaiting_revoke_and_ack(peer->channel)) {
+		tal_free(tmpctx);
+		return;
+	}
+
 	/* BOLT #2:
 	 *
 	 * A node MUST NOT send a `commitment_signed` message which does not