MANIFEST                     |  1 +
 lib/PublicInbox/LeiMirror.pm | 28 +++++++++++++++++++++-------
 t/lei-mirror.psgi            |  9 +++++++++
 t/lei-mirror.t               |  6 +++++-

diff --git a/MANIFEST b/MANIFEST
index 531f8c46dc4b62252ac171abbfc7002f6d8479cc..a22672e713557172af655620bce32a8038cdeb6f 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -436,6 +436,7 @@ t/lei-import-nntp.t
 t/lei-import.t
 t/lei-index.t
 t/lei-lcat.t
+t/lei-mirror.psgi
 t/lei-mirror.t
 t/lei-p2q.t
 t/lei-q-kw.t
diff --git a/lib/PublicInbox/LeiMirror.pm b/lib/PublicInbox/LeiMirror.pm
index 39671f902b5514b19657bb7e937a06c935aca76d..fca11ccff037cae4d5b1f4b37e609c36733629fa 100644
--- a/lib/PublicInbox/LeiMirror.pm
+++ b/lib/PublicInbox/LeiMirror.pm
@@ -200,6 +200,19 @@ 	undef $on_destroy; # unlock
 	index_cloned_inbox($self, 2);
 }
 
+# PSGI mount prefixes and manifest.js.gz prefixes don't always align...
+sub deduce_epochs ($$) {
+	my ($m, $path) = @_;
+	my ($v1_bare, @v2_epochs);
+	my $path_pfx = '';
+	do {
+		$v1_bare = $m->{$path};
+		@v2_epochs = grep(m!\A\Q$path\E/git/[0-9]+\.git\z!, keys %$m);
+	} while (!defined($v1_bare) && !@v2_epochs &&
+		$path =~ s!\A(/[^/]+)/!/! and $path_pfx .= $1);
+	($path_pfx, $v1_bare, @v2_epochs);
+}
+
 sub try_manifest {
 	my ($self) = @_;
 	my $uri = URI->new($self->{src});
@@ -229,8 +242,7 @@ 	my $m = eval { PublicInbox::Config->json->decode($js) };
 	die "$uri: error decoding `$js': $@" if $@;
 	ref($m) eq 'HASH' or die "$uri unknown type: ".ref($m);
 
-	my $v1_bare = $m->{$path};
-	my @v2_epochs = grep(m!\A\Q$path\E/git/[0-9]+\.git\z!, keys %$m);
+	my ($path_pfx, $v1_bare, @v2_epochs) = deduce_epochs($m, $path);
 	if (@v2_epochs) {
 		# It may be possible to have v1 + v2 in parallel someday:
 		$lei->err(<<EOM) if defined $v1_bare;
@@ -238,14 +250,16 @@ # `$v1_bare' appears to be a v1 inbox while v2 epochs exist:
 # @v2_epochs
 # ignoring $v1_bare (use --inbox-version=1 to force v1 instead)
 EOM
-		@v2_epochs = map { $uri->path($_); $uri->clone } @v2_epochs;
+		@v2_epochs = map {
+			$uri->path($path_pfx.$_);
+			$uri->clone
+		} @v2_epochs;
 		clone_v2($self, \@v2_epochs);
-	} elsif ($v1_bare) {
+	} elsif (defined $v1_bare) {
 		clone_v1($self);
-	} elsif (my @maybe = grep(m!\Q$path\E!, keys %$m)) {
-		die "E: confused by <$uri>, possible matches:\n@maybe";
 	} else {
-		die "E: confused by <$uri>";
+		die "E: confused by <$uri>, possible matches:\n\t",
+			join(', ', sort keys %$m), "\n";
 	}
 }
 
diff --git a/t/lei-mirror.psgi b/t/lei-mirror.psgi
new file mode 100644
index 0000000000000000000000000000000000000000..6b4bbfecc3e241b6b375191da5172fd0bfc5679e
--- /dev/null
+++ b/t/lei-mirror.psgi
@@ -0,0 +1,9 @@
+use Plack::Builder;
+use PublicInbox::WWW;
+my $www = PublicInbox::WWW->new;
+$www->preload;
+builder {
+	enable 'Head';
+	mount '/pfx' => builder { sub { $www->call(@_) } };
+	mount '/' => builder { sub { $www->call(@_) } };
+};
diff --git a/t/lei-mirror.t b/t/lei-mirror.t
index 80bc6ed5ab135f266addc9e63c9bbd2fc7e276de..65b6068ccb917af1ef7992eed14d6276ecd916af 100644
--- a/t/lei-mirror.t
+++ b/t/lei-mirror.t
@@ -7,7 +7,8 @@ my $sock = tcp_server();
 my ($tmpdir, $for_destroy) = tmpdir();
 my $http = 'http://'.tcp_host_port($sock);
 my ($ro_home, $cfg_path) = setup_public_inboxes;
-my $cmd = [ qw(-httpd -W0), "--stdout=$tmpdir/out", "--stderr=$tmpdir/err" ];
+my $cmd = [ qw(-httpd -W0 ./t/lei-mirror.psgi),
+	"--stdout=$tmpdir/out", "--stderr=$tmpdir/err" ];
 my $td = start_script($cmd, { PI_CONFIG => $cfg_path }, { 3 => $sock });
 test_lei({ tmpdir => $tmpdir }, sub {
 	my $home = $ENV{HOME};
@@ -42,6 +43,9 @@ 	like($lei_err, qr/not a directory/, 'non-directory noted');
 	ok(!-d "$t2-fail", 'destination not created on failure');
 	lei_ok('ls-external');
 	unlike($lei_out, qr!\Q$t2-fail\E!, 'not added to ls-external');
+
+	lei_ok('add-external', "$t1-pfx", '--mirror', "$http/pfx/t1/",
+			\'--mirror v1 w/ PSGI prefix');
 
 	my %phail = (
 		HTTPS => 'https://public-inbox.org/' . 'phail',