new file mode 100644
--- /dev/null
+++ b/proxy_merge_headers.t
@@ -0,0 +1,111 @@
+#!/usr/bin/perl
+
+# (C) Maxim Dounin
+
+# Tests for proxy_set_header inheritance.
+
+###############################################################################
+
+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 $t = Test::Nginx->new()->has(qw/http proxy cache rewrite/)->plan(3)
+	->write_file_expand('nginx.conf', <<'EOF');
+
+%%TEST_GLOBALS%%
+
+daemon         off;
+
+events {
+}
+
+http {
+    %%TEST_GLOBALS_HTTP%%
+
+    proxy_cache_path   %%TESTDIR%%/cache  levels=1:2
+                       keys_zone=NAME:10m;
+
+    proxy_set_header X-Blah "blah";
+
+    server {
+        listen       127.0.0.1:8080;
+        server_name  localhost;
+
+        proxy_cache  NAME;
+
+        location / {
+            proxy_pass    http://127.0.0.1:8081;
+        }
+
+        location /no/ {
+            proxy_pass    http://127.0.0.1:8081;
+            proxy_cache   off;
+        }
+
+        location /setbody/ {
+            proxy_pass    http://127.0.0.1:8081;
+            proxy_set_body "body";
+        }
+    }
+
+    server {
+        listen       127.0.0.1:8081;
+        server_name  localhost;
+
+        location / {
+            return 200 "ims=$http_if_modified_since;blah=$http_x_blah;";
+        }
+    }
+}
+
+EOF
+
+$t->run();
+
+###############################################################################
+
+like(http_get_ims('/'), qr/ims=;blah=blah;/,
+	'if-modified-since cleared with cache');
+
+TODO: {
+local $TODO = 'not yet';
+
+like(http_get_ims('/no/'), qr/ims=blah;blah=blah;/,
+	'if-modified-since preserved without cache');
+
+}
+
+TODO: {
+local $TODO = 'not yet';
+
+like(http_get_ims('/setbody/'), qr/blah=blah;/,
+	'proxy_set_header inherited with proxy_set_body');
+
+}
+
+###############################################################################
+
+sub http_get_ims {
+        my ($url) = @_;
+        return http(<<EOF);
+GET $url HTTP/1.0
+Host: localhost
+Connection: close
+If-Modified-Since: blah
+
+EOF
+}
+
+###############################################################################