lib/PublicInbox/ExtMsg.pm            | 2 +-
 lib/PublicInbox/Search.pm            | 8 ++++----
 lib/PublicInbox/SearchIdx.pm         | 8 ++++----
 lib/PublicInbox/SearchIdxSkeleton.pm | 2 +-
 lib/PublicInbox/SearchMsg.pm         | 2 +-

diff --git a/lib/PublicInbox/ExtMsg.pm b/lib/PublicInbox/ExtMsg.pm
index 90d68db8fd68ac7bbe8cafca3f7ded8c645c8781..f3076a3476daef7022f66408a8b9cc6f4b1a0352 100644
--- a/lib/PublicInbox/ExtMsg.pm
+++ b/lib/PublicInbox/ExtMsg.pm
@@ -46,7 +46,7 @@ 			return;
 		}
 
 		# try to find the URL with Xapian to avoid forking
-		my $doc_id = eval { $s->find_first_doc_id('XMID' . $mid) };
+		my $doc_id = eval { $s->find_first_doc_id('Q' . $mid) };
 		if ($@) {
 			# xapian not configured properly for this repo
 			push @nox, $other;
diff --git a/lib/PublicInbox/Search.pm b/lib/PublicInbox/Search.pm
index c074410c5bf24188d471c6fae100e2acf3df9c9b..74f406adfcf8da63654ec8394d8807b188f8156c 100644
--- a/lib/PublicInbox/Search.pm
+++ b/lib/PublicInbox/Search.pm
@@ -56,7 +56,7 @@ 	thread => 'G', # newsGroup (or similar entity - e.g. a web forum name)
 );
 
 my %bool_pfx_external = (
-	mid => 'XMID', # Message-ID (full/exact)
+	mid => 'Q', # Message-ID (full/exact), this is mostly uniQue
 );
 
 my %prob_prefix = (
@@ -333,7 +333,7 @@ sub lookup_skeleton {
 	my ($self, $mid) = @_;
 	my $skel = $self->{skel} or return lookup_message($self, $mid);
 	$mid = mid_clean($mid);
-	my $term = 'XMID' . $mid;
+	my $term = 'Q' . $mid;
 	my $smsg;
 	my $beg = $skel->postlist_begin($term);
 	if ($beg != $skel->postlist_end($term)) {
@@ -352,7 +352,7 @@ sub lookup_message {
 	my ($self, $mid) = @_;
 	$mid = mid_clean($mid);
 
-	my $doc_id = $self->find_first_doc_id('XMID' . $mid);
+	my $doc_id = $self->find_first_doc_id('Q' . $mid);
 	my $smsg;
 	if (defined $doc_id) {
 		# raises on error:
@@ -377,7 +377,7 @@ 	$mid = mid_clean($mid);
 	my $xdb = $self->{xdb};
 	# XXX retry_reopen isn't necessary for V2Writable, but the PSGI
 	# interface will need it...
-	my ($head, $tail) = $self->find_doc_ids('XMID' . $mid);
+	my ($head, $tail) = $self->find_doc_ids('Q' . $mid);
 	for (; $head->nequal($tail); $head->inc) {
 		my $doc_id = $head->get_docid;
 		my $doc = $xdb->get_document($doc_id);
diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 57aed75c31d154b79499eabb93b588f2829d6213..61dc0577f553e21a064d522a0d7b4b9c4a46c091 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -19,7 +19,7 @@ use POSIX qw(strftime);
 require PublicInbox::Git;
 
 use constant {
-	MAX_MID_SIZE => 244, # max term size - 1 in Xapian
+	MAX_MID_SIZE => 244, # max term size (Xapian limitation) - length('Q')
 	PERM_UMASK => 0,
 	OLD_PERM_GROUP => 1,
 	OLD_PERM_EVERYBODY => 2,
@@ -302,7 +302,7 @@ 			$old_tid = $smsg->thread_id unless $skel;
 		}
 		$smsg = PublicInbox::SearchMsg->new($mime);
 		my $doc = $smsg->{doc};
-		$doc->add_term('XMID' . $mid);
+		$doc->add_term('Q' . $mid);
 
 		my $subj = $smsg->subject;
 		my $xpath;
@@ -404,7 +404,7 @@ 	my $doc_id;
 	$mid = mid_clean($mid);
 
 	eval {
-		my ($head, $tail) = $self->find_doc_ids('XMID' . $mid);
+		my ($head, $tail) = $self->find_doc_ids('Q' . $mid);
 		if ($head->equal($tail)) {
 			warn "cannot remove non-existent <$mid>\n";
 		}
@@ -721,7 +721,7 @@ 	my ($self, $mid) = @_;
 
 	my $tid = $self->next_thread_id;
 	my $doc = Search::Xapian::Document->new;
-	$doc->add_term('XMID' . $mid);
+	$doc->add_term('Q' . $mid);
 	$doc->add_term('G' . $tid);
 	$doc->add_term('T' . 'ghost');
 
diff --git a/lib/PublicInbox/SearchIdxSkeleton.pm b/lib/PublicInbox/SearchIdxSkeleton.pm
index aa2713f12743b58944badaa003e67b7215430c68..333f965d49b6c893e870b738d5d8f5012a8a60ad 100644
--- a/lib/PublicInbox/SearchIdxSkeleton.pm
+++ b/lib/PublicInbox/SearchIdxSkeleton.pm
@@ -107,7 +107,7 @@ 		$smsg->{mid} = $mid;
 	}
 	my $doc = $smsg->{doc};
 	$doc->add_term('XPATH' . $xpath) if defined $xpath;
-	$doc->add_term('XMID' . $mid);
+	$doc->add_term('Q' . $mid);
 	PublicInbox::SearchIdx::add_values($doc, $values);
 	$doc->set_data($doc_data);
 	$smsg->{ts} = $ts;
diff --git a/lib/PublicInbox/SearchMsg.pm b/lib/PublicInbox/SearchMsg.pm
index 941bfd24128ae417ed919d0db9d8c1a68d3e8d97..014f4909d90e9415da3bbde17829e5c8dffea42d 100644
--- a/lib/PublicInbox/SearchMsg.pm
+++ b/lib/PublicInbox/SearchMsg.pm
@@ -154,7 +154,7 @@ 		$self->{mid} = $mid;
 	} elsif (my $rv = $self->{mid}) {
 		$rv;
 	} else {
-		$self->{mid} = _get_term_val($self, 'XMID', qr/\AXMID/) ||
+		$self->{mid} = _get_term_val($self, 'Q', qr/\AQ/) ||
 				$self->_extract_mid;
 	}
 }