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

diff --git a/lib/PublicInbox/Search.pm b/lib/PublicInbox/Search.pm
index 9ab5afe6d619860a1277314b5680350a109897b8..3ec96ca93a35fc966166c3c08ebb872cf3fb27d1 100644
--- a/lib/PublicInbox/Search.pm
+++ b/lib/PublicInbox/Search.pm
@@ -56,13 +56,13 @@ 	thread => 'G', # newsGroup (or similar entity - e.g. a web forum name)
 );
 
 my %bool_pfx_external = (
-	mid => 'Q', # uniQue id (Message-ID)
+	mid => 'XMID', # uniQue id (Message-ID)
 );
 
 my %prob_prefix = (
 	# for mairix compatibility
 	s => 'S',
-	m => 'XMID', # 'mid:' (bool) is exact, 'm:' (prob) can do partial
+	m => 'XM', # 'mid:' (bool) is exact, 'm:' (prob) can do partial
 	f => 'A',
 	t => 'XTO',
 	tc => 'XTO XCC',
@@ -85,7 +85,7 @@ 	dfpost => 'XDFPOST',
 	dfblob => 'XDFPRE XDFPOST',
 
 	# default:
-	'' => 'XMID S A XNQ XQUOT XFN',
+	'' => 'XM S A XNQ XQUOT XFN',
 );
 
 # not documenting m: and mid: for now, the using the URLs works w/o Xapian
@@ -285,7 +285,7 @@ sub lookup_message {
 	my ($self, $mid) = @_;
 	$mid = mid_clean($mid);
 
-	my $doc_id = $self->find_unique_doc_id('Q' . $mid);
+	my $doc_id = $self->find_unique_doc_id('XMID' . $mid);
 	my $smsg;
 	if (defined $doc_id) {
 		# raises on error:
diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 66faed312c3243f1a56789c898b7d5bd4dd6e4a3..0ee077910c8b0d6f0ff7837d69250daf18e86037 100644
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -276,7 +276,7 @@ 			$old_tid = $smsg->thread_id;
 		}
 		$smsg = PublicInbox::SearchMsg->new($mime);
 		my $doc = $smsg->{doc};
-		$doc->add_term('Q' . $mid);
+		$doc->add_term('XMID' . $mid);
 
 		my $subj = $smsg->subject;
 		if ($subj ne '') {
@@ -334,7 +334,7 @@ 			index_body($tg, \@orig, $doc) if @orig;
 		});
 
 		link_message($self, $smsg, $old_tid);
-		$tg->index_text($mid, 1, 'XMID');
+		$tg->index_text($mid, 1, 'XM');
 		$doc->set_data($smsg->to_doc_data($blob));
 
 		if (my $altid = $self->{-altid}) {
@@ -366,7 +366,7 @@ 	my $doc_id;
 	$mid = mid_clean($mid);
 
 	eval {
-		$doc_id = $self->find_unique_doc_id('Q' . $mid);
+		$doc_id = $self->find_unique_doc_id('XMID' . $mid);
 		if (defined $doc_id) {
 			$db->delete_document($doc_id);
 		} else {
@@ -683,7 +683,7 @@ 	my ($self, $mid) = @_;
 
 	my $tid = $self->next_thread_id;
 	my $doc = Search::Xapian::Document->new;
-	$doc->add_term('Q' . $mid);
+	$doc->add_term('XMID' . $mid);
 	$doc->add_term('G' . $tid);
 	$doc->add_term('T' . 'ghost');
 
diff --git a/lib/PublicInbox/SearchMsg.pm b/lib/PublicInbox/SearchMsg.pm
index 70aa70674f8da9a8cd62145b9ed726d484f087e6..25c1abb863ca6b951a698a3cf5b0f7a8e732b989 100644
--- a/lib/PublicInbox/SearchMsg.pm
+++ b/lib/PublicInbox/SearchMsg.pm
@@ -157,7 +157,7 @@ 		$self->{mid} = $mid;
 	} elsif (my $rv = $self->{mid}) {
 		$rv;
 	} else {
-		$self->{mid} = _get_term_val($self, 'Q', qr/\AQ/) ||
+		$self->{mid} = _get_term_val($self, 'XMID', qr/\AXMID/) ||
 				$self->_extract_mid;
 	}
 }