lib/PublicInbox/Inbox.pm | 2 +-
 t/inbox.t                | 3 +++

diff --git a/lib/PublicInbox/Inbox.pm b/lib/PublicInbox/Inbox.pm
index 27218de74c22a9082dba5d10942186fe29947752..c982d0b41bc2212211164a333de8ff82d3385563 100644
--- a/lib/PublicInbox/Inbox.pm
+++ b/lib/PublicInbox/Inbox.pm
@@ -73,7 +73,7 @@ 		$url .= $self->{name} . '/';
 	} else {
 		# either called from a non-PSGI environment (e.g. NNTP/POP3)
 		$self->{-base_url} ||= do {
-			my $url = $self->{url};
+			my $url = $self->{url} or return undef;
 			# expand protocol-relative URLs to HTTPS if we're
 			# not inside a web server
 			$url = "https:$url" if $url =~ m!\A//!;
diff --git a/t/inbox.t b/t/inbox.t
index 45ba1df2e5576496c164807378f98857676c8272..9909dc530fbdd964b6b0bbd787abd4cc2bd5834f 100644
--- a/t/inbox.t
+++ b/t/inbox.t
@@ -9,4 +9,7 @@ is($x->base_url, 'https://example.com/test/', 'expanded protocol-relative');
 $x = PublicInbox::Inbox->new({url => 'http://example.com/test'});
 is($x->base_url, 'http://example.com/test/', 'added trailing slash');
 
+$x = PublicInbox::Inbox->new({});
+is($x->base_url, undef, 'undef base_url allowed');
+
 done_testing();