lib/PublicInbox/Search.pm    | 3 ++-
 lib/PublicInbox/SearchIdx.pm | 5 +++--

diff --git a/lib/PublicInbox/Search.pm b/lib/PublicInbox/Search.pm
index 8c0bab185d489008356e8efeafa641893549eac7..bf50365a04603d86d9722a923e4a36f0b8287c77 100644
--- a/lib/PublicInbox/Search.pm
+++ b/lib/PublicInbox/Search.pm
@@ -36,7 +36,8 @@ 	# 7 - remove references and inreplyto terms
 	# 8 - remove redundant/unneeded document data
 	# 9 - disable Message-ID compression (SHA-1)
 	# 10 - optimize doc for NNTP overviews
-	SCHEMA_VERSION => 10,
+	# 11 - merge threads when vivifying ghosts
+	SCHEMA_VERSION => 11,
 
 	# n.b. FLAG_PURE_NOT is expensive not suitable for a public website
 	# as it could become a denial-of-service vector
diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 31346876bcfefdd1f123d2537e1a06313db1e2cc..58eccc1a2d67241ed273e940fee0d1fb2b27c51d 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -150,7 +150,7 @@ 		});
 
 		if ($was_ghost) {
 			$doc_id = $smsg->doc_id;
-			$self->link_message($smsg);
+			$self->link_message($smsg, $smsg->thread_id);
 			$doc->set_data($smsg->to_doc_data);
 			$db->replace_document($doc_id, $doc);
 		} else {
@@ -211,7 +211,7 @@ 	$last_thread_id;
 }
 
 sub link_message {
-	my ($self, $smsg) = @_;
+	my ($self, $smsg, $old_tid) = @_;
 	my $doc = $smsg->{doc};
 	my $mid = $smsg->mid;
 	my $mime = $smsg->mime;
@@ -247,6 +247,7 @@ 		# first ref *should* be the thread root,
 		# but we can never trust clients to do the right thing
 		my $ref = shift @refs;
 		$tid = $self->_resolve_mid_to_tid($ref);
+		$self->merge_threads($tid, $old_tid) if defined $old_tid;
 
 		# the rest of the refs should point to this tid:
 		foreach $ref (@refs) {