Do not update peer information if ancestor search is in progress

client/network/sync/src/lib.rs

@@ -2043,17 +2043,17 @@ where
 			return PollBlockAnnounceValidation::Nothing { is_best, who, announce }
 		};
 
+		if let PeerSyncState::AncestorSearch { .. } = peer.state {
+			trace!(target: "sync", "Peer state is ancestor search.");
+			return PollBlockAnnounceValidation::Nothing { is_best, who, announce }
+		}
+
 		if is_best {
 			// update their best block
 			peer.best_number = number;
 			peer.best_hash = hash;
 		}
 
-		if let PeerSyncState::AncestorSearch { .. } = peer.state {
-			trace!(target: "sync", "Peer state is ancestor search.");
-			return PollBlockAnnounceValidation::Nothing { is_best, who, announce }
-		}
-
 		// If the announced block is the best they have and is not ahead of us, our common number
 		// is either one further ahead or it's the one they just announced, if we know about it.
 		if is_best {

client/network/test/src/sync.rs

@@ -558,6 +558,10 @@ fn syncs_header_only_forks() {
 	while !net.peer(1).has_block(&small_hash) {
 		net.block_until_idle();
 	}
+
+	net.block_until_sync();
+	assert_eq!(net.peer(0).client().info().best_hash, net.peer(1).client().info().best_hash);
+	assert_ne!(small_hash, net.peer(0).client().info().best_hash);
 }
 
 #[test]