lib/PublicInbox/WatchMaildir.pm | 13 +++++++++----
 t/watch_maildir.t               |  9 +++++++++

diff --git a/lib/PublicInbox/WatchMaildir.pm b/lib/PublicInbox/WatchMaildir.pm
index 8d8e817ad767d9097b438c84ae336ea503e12a4b..84080ba958f0dfd629743834761a87f82f6cbc9e 100644
--- a/lib/PublicInbox/WatchMaildir.pm
+++ b/lib/PublicInbox/WatchMaildir.pm
@@ -28,8 +28,7 @@ 	# indefinitely...
 	foreach my $pfx (qw(publicinboxwatch publicinboxlearn)) {
 		my $k = "$pfx.watchspam";
 		if (my $dir = $config->{$k}) {
-			if ($dir =~ s/\Amaildir://) {
-				$dir =~ s!/+\z!!;
+			if (is_maildir($dir)) {
 				# skip "new", no MUA has seen it, yet.
 				my $cur = "$dir/cur";
 				my $old = $mdmap{$cur};
@@ -60,8 +59,7 @@ 		# need to make all inboxes writable for spam removal:
 		my $ibx = $_[0] = PublicInbox::InboxWritable->new($_[0]);
 
 		my $watch = $ibx->{watch} or return;
-		if ($watch =~ s/\Amaildir://) {
-			$watch =~ s!/+\z!!;
+		if (is_maildir($watch)) {
 			if (my $wm = $ibx->{watchheader}) {
 				my ($k, $v) = split(/:/, $wm, 2);
 				$ibx->{-watchheader} = [ $k, qr/\Q$v\E/ ];
@@ -276,6 +274,13 @@ 		}
 		warn $mime->header('Message-ID')." failed spam check\n";
 		undef;
 	}
+}
+
+sub is_maildir {
+	$_[0] =~ s!\Amaildir:!! or return;
+	$_[0] =~ tr!/!/!s;
+	$_[0] =~ s!/\z!!;
+	$_[0];
 }
 
 1;
diff --git a/t/watch_maildir.t b/t/watch_maildir.t
index 7178f29efe029e4815a30d2098790b9a0d07b08a..b85ddc580a69b6f6a1121941fb4d23be3156bc96 100644
--- a/t/watch_maildir.t
+++ b/t/watch_maildir.t
@@ -124,4 +124,13 @@ 	my $mref = $git->cat_file('refs/heads/master:'.$list[0]);
 	like($$mref, qr/something\n\z/s, 'message scrubbed on import');
 }
 
+sub is_maildir {
+	my ($dir) = @_;
+	PublicInbox::WatchMaildir::is_maildir($dir);
+}
+
+is(is_maildir('maildir:/hello//world'), '/hello/world', 'extra slash gone');
+is(is_maildir('maildir:/hello/world/'), '/hello/world', 'trailing slash gone');
+is(is_maildir('faildir:/hello/world/'), undef, 'non-maildir rejected');
+
 done_testing;