diff --git a/src/shrpx.cc b/src/shrpx.cc
index 4eee9795..f9d9c3bf 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -28,6 +28,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/socket.h>
+#include <sys/un.h>
 #include <netdb.h>
 #include <signal.h>
 #include <netinet/in.h>
@@ -821,7 +822,9 @@ Connections:
               backend addresses are accepted by repeating this option.
               HTTP/2  backend   does  not  support   multiple  backend
               addresses  and the  first occurrence  of this  option is
-              used.
+              used.  UNIX domain socket  can be specified by prefixing
+              path        name        with       "unix:"        (e.g.,
+              -bunix:/var/run/backend.sock)
               Default: )" << DEFAULT_DOWNSTREAM_HOST << ","
       << DEFAULT_DOWNSTREAM_PORT << R"(
   -f, --frontend=<HOST,PORT>
@@ -1870,23 +1873,35 @@ int main(int argc, char **argv) {
   }
 
   for (auto &addr : mod_config()->downstream_addrs) {
-    auto ipv6 = util::ipv6_numeric_addr(addr.host.get());
-    std::string hostport;
 
-    if (ipv6) {
-      hostport += "[";
+    if (util::istartsWith(addr.host.get(), SHRPX_UNIX_PATH_PREFIX)) {
+      // for AF_UNIX socket, we use "localhost" as host for backend
+      // hostport.  This is used as Host header field to backend and
+      // not going to be passed to any syscalls.
+      addr.hostport =
+          strcopy(util::make_hostport("localhost", get_config()->port));
+
+      auto path = addr.host.get() + str_size(SHRPX_UNIX_PATH_PREFIX);
+      auto pathlen = strlen(path);
+
+      if (pathlen + 1 > sizeof(addr.addr.un.sun_path)) {
+        LOG(FATAL) << "path unix domain socket is bound to is too long > "
+                   << sizeof(addr.addr.un.sun_path);
+        exit(EXIT_FAILURE);
+      }
+
+      LOG(INFO) << "Use UNIX domain socket path " << path
+                << " for backend connection";
+
+      addr.addr.un.sun_family = AF_UNIX;
+      // copy path including terminal NULL
+      std::copy_n(path, pathlen + 1, addr.addr.un.sun_path);
+      addr.addrlen = sizeof(addr.addr.un);
+
+      continue;
     }
 
-    hostport += addr.host.get();
-
-    if (ipv6) {
-      hostport += "]";
-    }
-
-    hostport += ":";
-    hostport += util::utos(addr.port);
-
-    addr.hostport = strcopy(hostport);
+    addr.hostport = strcopy(util::make_hostport(addr.host.get(), addr.port));
 
     if (resolve_hostname(
             &addr.addr, &addr.addrlen, addr.host.get(), addr.port,
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 96775a03..5e87b390 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -521,6 +521,16 @@ int parse_config(const char *opt, const char *optarg) {
   char host[NI_MAXHOST];
   uint16_t port;
   if (util::strieq(opt, SHRPX_OPT_BACKEND)) {
+    if (util::istartsWith(optarg, SHRPX_UNIX_PATH_PREFIX)) {
+      DownstreamAddr addr;
+      addr.host = strcopy(optarg);
+      addr.port = 0;
+
+      mod_config()->downstream_addrs.push_back(std::move(addr));
+
+      return 0;
+    }
+
     if (split_host_port(host, sizeof(host), &port, optarg) == -1) {
       return -1;
     }
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index e2c75514..5bb05861 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -30,6 +30,7 @@
 #include <stdint.h>
 #include <sys/types.h>
 #include <sys/socket.h>
+#include <sys/un.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <cstdio>
@@ -52,6 +53,8 @@ class CertLookupTree;
 
 } // namespace ssl
 
+#define SHRPX_UNIX_PATH_PREFIX "unix:"
+
 extern const char SHRPX_OPT_PRIVATE_KEY_FILE[];
 extern const char SHRPX_OPT_PRIVATE_KEY_PASSWD_FILE[];
 extern const char SHRPX_OPT_CERTIFICATE_FILE[];
@@ -139,6 +142,7 @@ union sockaddr_union {
   sockaddr sa;
   sockaddr_in6 in6;
   sockaddr_in in;
+  sockaddr_un un;
 };
 
 enum shrpx_proto { PROTO_HTTP2, PROTO_HTTP };
diff --git a/src/util.cc b/src/util.cc
index 72301216..465ea411 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -847,7 +847,9 @@ int create_nonblock_socket(int family) {
   make_socket_closeonexec(fd);
 #endif // !SOCK_NONBLOCK
 
-  make_socket_nodelay(fd);
+  if (family == AF_INET || family == AF_INET6) {
+    make_socket_nodelay(fd);
+  }
 
   return fd;
 }
@@ -1016,6 +1018,26 @@ std::string dtos(double n) {
   return utos(static_cast<int64_t>(n)) + "." + (f.size() == 1 ? "0" : "") + f;
 }
 
+std::string make_hostport(const char *host, uint16_t port) {
+  auto ipv6 = ipv6_numeric_addr(host);
+  std::string hostport;
+
+  if (ipv6) {
+    hostport += "[";
+  }
+
+  hostport += host;
+
+  if (ipv6) {
+    hostport += "]";
+  }
+
+  hostport += ":";
+  hostport += utos(port);
+
+  return hostport;
+}
+
 } // namespace util
 
 } // namespace nghttp2
diff --git a/src/util.h b/src/util.h
index c396a7c3..1345ba18 100644
--- a/src/util.h
+++ b/src/util.h
@@ -551,6 +551,11 @@ std::string duration_str(double t);
 // fractional digits follow.
 std::string format_duration(const std::chrono::microseconds &u);
 
+// Creates "host:port" string using given |host| and |port|.  If
+// |host| is numeric IPv6 address (e.g., ::1), it is enclosed by "["
+// and "]".
+std::string make_hostport(const char *host, uint16_t port);
+
 } // namespace util
 
 } // namespace nghttp2