new file mode 100644
--- /dev/null
+++ b/not-modified.t
@@ -0,0 +1,88 @@
+#!/usr/bin/perl
+
+# (C) Maxim Dounin
+
+# Tests for not modified filter module.
+
+###############################################################################
+
+use warnings;
+use strict;
+
+use Test::More;
+
+BEGIN { use FindBin; chdir($FindBin::Bin); }
+
+use lib 'lib';
+use Test::Nginx;
+
+###############################################################################
+
+select STDERR; $| = 1;
+select STDOUT; $| = 1;
+
+my $t = Test::Nginx->new()->plan(4)
+	->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+master_process off;
+daemon         off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    server {
+        listen       127.0.0.1:8080;
+        server_name  localhost;
+
+        location / {
+            if_modified_since before;
+        }
+    }
+}
+
+EOF
+
+$t->write_file('t', '');
+
+$t->run();
+
+###############################################################################
+
+like(http_get_ims('/t', 'Wed, 08 Jul 2037 22:53:52 GMT'), qr/304/,
+	'0x7F000000');
+
+TODO: {
+local $TODO = 'not yet';
+
+like(http_get_ims('/t', 'Tue, 19 Jan 2038 03:14:07 GMT'), qr/304/,
+	'0x7FFFFFFF');
+
+}
+
+SKIP: {
+	skip "only for 32-bit time_t", 2 if (gmtime(0xFFFFFFFF))[5] == 206;
+
+	like(http_get_ims('/t', 'Tue, 19 Jan 2038 03:14:08 GMT'), qr/200/,
+		'0x7FFFFFFF + 1');
+	like(http_get_ims('/t', 'Fri, 25 Feb 2174 09:42:23 GMT'), qr/200/,
+		'0x17FFFFFFF');
+}
+
+###############################################################################
+
+sub http_get_ims {
+        my ($url, $ims) = @_;
+        return http(<<EOF);
+GET $url HTTP/1.0
+Host: localhost
+If-Modified-Since: $ims
+
+EOF
+}
+
+###############################################################################