diff --git a/common/gossmap.c b/common/gossmap.c
index 4eef0426d..dd834b639 100644
--- a/common/gossmap.c
+++ b/common/gossmap.c
@@ -1444,3 +1444,9 @@ u8 *gossmap_node_get_features(const tal_t *ctx,
 	map_copy(map, n->nann_off + feature_len_off + 2, ret, feature_len);
 	return ret;
 }
+
+size_t gossmap_lengths(const struct gossmap *map, size_t *total)
+{
+	*total = map->map_size;
+	return map->map_end;
+}
diff --git a/common/gossmap.h b/common/gossmap.h
index c2a86b321..b42045337 100644
--- a/common/gossmap.h
+++ b/common/gossmap.h
@@ -257,4 +257,7 @@ size_t gossmap_num_chans(const struct gossmap *map);
 struct gossmap_chan *gossmap_first_chan(const struct gossmap *map);
 struct gossmap_chan *gossmap_next_chan(const struct gossmap *map,
 				       struct gossmap_chan *prev);
+
+/* For debugging: returns length read, and total known length of file */
+size_t gossmap_lengths(const struct gossmap *map, size_t *total);
 #endif /* LIGHTNING_COMMON_GOSSMAP_H */
diff --git a/gossipd/gossip_store.c b/gossipd/gossip_store.c
index b7362cbef..14c41af7d 100644
--- a/gossipd/gossip_store.c
+++ b/gossipd/gossip_store.c
@@ -600,3 +600,8 @@ void gossip_store_set_timestamp(struct gossip_store *gs, u64 offset, u32 timesta
 			      "Failed writing header to re-timestamp @%"PRIu64": %s",
 			      offset, strerror(errno));
 }
+
+u64 gossip_store_len_written(const struct gossip_store *gs)
+{
+	return gs->len;
+}
diff --git a/gossipd/gossip_store.h b/gossipd/gossip_store.h
index 8e38dc6ab..ba85e78a8 100644
--- a/gossipd/gossip_store.h
+++ b/gossipd/gossip_store.h
@@ -113,4 +113,8 @@ u32 gossip_store_get_timestamp(struct gossip_store *gs, u64 offset);
  */
 void gossip_store_set_timestamp(struct gossip_store *gs, u64 offset, u32 timestamp);
 
+/**
+ * For debugging.
+ */
+u64 gossip_store_len_written(const struct gossip_store *gs);
 #endif /* LIGHTNING_GOSSIPD_GOSSIP_STORE_H */
diff --git a/gossipd/gossmap_manage.c b/gossipd/gossmap_manage.c
index 884acfb10..4ded33768 100644
--- a/gossipd/gossmap_manage.c
+++ b/gossipd/gossmap_manage.c
@@ -652,6 +652,34 @@ void gossmap_manage_handle_get_txout_reply(struct gossmap_manage *gm, const u8 *
 		goto bad;
 	}
 
+	/* We have reports of doubled-up channel_announcements, hence this check! */
+	struct gossmap_chan *chan;
+	size_t before_length_processed, before_total_length;
+
+	before_length_processed = gossmap_lengths(gm->raw_gossmap, &before_total_length);
+	chan = gossmap_find_chan(gm->raw_gossmap, &scid);
+	if (chan) {
+		status_broken("Redundant channel_announce for scid %s at off %u (gossmap %zu/%zu, store %"PRIu64")",
+			      fmt_short_channel_id(tmpctx, scid), chan->cann_off,
+			      before_length_processed, before_total_length,
+			      gossip_store_len_written(gm->daemon->gs));
+		goto out;
+	} else {
+		size_t after_length_processed, after_total_length;
+		/* Good, now try refreshing in case it somehow slipped in! */
+		gossmap = gossmap_manage_get_gossmap(gm);
+		after_length_processed = gossmap_lengths(gm->raw_gossmap, &after_total_length);
+		chan = gossmap_find_chan(gm->raw_gossmap, &scid);
+		if (chan) {
+			status_broken("Redundant channel_announce *AFTER REFRESH* for scid %s at off %u (gossmap was %zu/%zu, now %zu/%zu, store %"PRIu64")",
+				      fmt_short_channel_id(tmpctx, scid), chan->cann_off,
+				      before_length_processed, before_total_length,
+				      after_length_processed, after_total_length,
+				      gossip_store_len_written(gm->daemon->gs));
+			goto out;
+		}
+	}
+
 	/* Set with timestamp 0 (we will update once we have a channel_update) */
 	gossip_store_add(gm->daemon->gs, pca->channel_announcement, 0);
 	gossip_store_add(gm->daemon->gs,
@@ -672,8 +700,9 @@ void gossmap_manage_handle_get_txout_reply(struct gossmap_manage *gm, const u8 *
 	return;
 
 bad:
-	tal_free(pca);
 	txout_failures_add(gm->txf, scid);
+out:
+	tal_free(pca);
 	/* If we looking specifically for this, we no longer are. */
 	remove_unknown_scid(gm->daemon->seeker, &scid, false);
 }