lib/PublicInbox/WwwStatic.pm | 10 ++++++++--
 xt/git-http-backend.t        | 20 ++++++++++++++++++++

diff --git a/lib/PublicInbox/WwwStatic.pm b/lib/PublicInbox/WwwStatic.pm
index 58db58b4e76755aac5ae8ad4f5d944865858d401..b8efcf625a184d03507161f570787f4547032f7a 100644
--- a/lib/PublicInbox/WwwStatic.pm
+++ b/lib/PublicInbox/WwwStatic.pm
@@ -4,6 +4,7 @@
 package PublicInbox::WwwStatic;
 use strict;
 use Fcntl qw(:seek);
+use HTTP::Date qw(time2str);
 
 sub prepare_range {
 	my ($env, $in, $h, $beg, $end, $size) = @_;
@@ -50,9 +51,14 @@ sub response {
 	my ($env, $h, $path, $type) = @_;
 	return unless -f $path && -r _; # just in case it's a FIFO :P
 
-	# TODO: If-Modified-Since and Last-Modified?
 	open my $in, '<', $path or return;
 	my $size = -s $in;
+	my $mtime = time2str((stat(_))[9]);
+
+	if (my $ims = $env->{HTTP_IF_MODIFIED_SINCE}) {
+		return [ 304, [], [] ] if $mtime eq $ims;
+	}
+
 	my $len = $size;
 	my $code = 200;
 	push @$h, 'Content-Type', $type;
@@ -63,7 +69,7 @@ 			push @$h, 'Content-Range', "bytes */$size";
 			return [ 416, $h, [] ];
 		}
 	}
-	push @$h, 'Content-Length', $len;
+	push @$h, 'Content-Length', $len, 'Last-Modified', $mtime;
 	my $body = bless {
 		initial_rd => 65536,
 		len => $len,
diff --git a/xt/git-http-backend.t b/xt/git-http-backend.t
index 421c6316ed43a31c346c3e9d744d32e788a41020..7f34d45213f69db4f227984bd97ab97a345821b8 100644
--- a/xt/git-http-backend.t
+++ b/xt/git-http-backend.t
@@ -8,6 +8,7 @@ use warnings;
 use Test::More;
 use POSIX qw(setsid);
 use PublicInbox::TestCommon;
+use PublicInbox::Spawn qw(which);
 
 my $git_dir = $ENV{GIANT_GIT_DIR};
 plan 'skip_all' => 'GIANT_GIT_DIR not defined' unless $git_dir;
@@ -72,6 +73,25 @@ 		my $diff = $get_maxrss->() - $mem_a;
 		note "${diff}K memory increase after $i seconds";
 		ok($diff < 1024, 'no bloating caused by slow dumb client');
 	}
+}
+
+SKIP: { # make sure Last-Modified + If-Modified-Since works with curl
+	my $nr = 6;
+	skip 'no description', $nr unless -f "$git_dir/description";
+	my $mtime = (stat(_))[9];
+	my $curl = which('curl');
+	skip 'curl(1) not found', $nr unless $curl;
+	my $url = "http://$host:$port/description";
+	my $dst = "$tmpdir/desc";
+	is(system($curl, qw(-RsSf), '-o', $dst, $url), 0, 'curl -R');
+	is((stat($dst))[9], $mtime, 'curl used remote mtime');
+	is(system($curl, qw(-sSf), '-z', $dst, '-o', "$dst.2", $url), 0,
+		'curl -z noop');
+	ok(!-e "$dst.2", 'no modification, nothing retrieved');
+	utime(0, 0, $dst) or die "utime failed: $!";
+	is(system($curl, qw(-sSfR), '-z', $dst, '-o', "$dst.2", $url), 0,
+		'curl -z updates');
+	ok(-e "$dst.2", 'faked modification, got new file retrieved');
 }
 
 {