diff --git a/doc/sources/libnghttp2_asio.rst b/doc/sources/libnghttp2_asio.rst
index c5c9bec9..bea4c536 100644
--- a/doc/sources/libnghttp2_asio.rst
+++ b/doc/sources/libnghttp2_asio.rst
@@ -42,7 +42,8 @@ HTTP/2 server looks like this:
 
       server.listen
         ("*", 3000,
-         [](std::shared_ptr<request> req, std::shared_ptr<response> res)
+         [](const std::shared_ptr<request>& req,
+            const std::shared_ptr<response>& res)
          {
            res->write_head(200);
            res->end("hello, world");
@@ -85,7 +86,8 @@ SSL/TLS.
 
       server.listen
         ("*", 3000,
-         [](std::shared_ptr<request> req, std::shared_ptr<response> res)
+         [](const std::shared_ptr<request>& req,
+            const std::shared_ptr<response>& res)
          {
            if(req->path() == "/" || req->path() == "/index.html") {
              res->write_head(200);
@@ -130,7 +132,8 @@ Server push is also supported.
 
       server.listen
         ("*", 3000,
-         [](std::shared_ptr<request> req, std::shared_ptr<response> res)
+         [](const std::shared_ptr<request>& req,
+            const std::shared_ptr<response>& res)
          {
            if(req->path() == "/") {
              req->push("GET", "/my.css");
@@ -202,7 +205,8 @@ blocking task there.  The example follows:
 
       server.listen
         ("*", 3000,
-         [](std::shared_ptr<request> req, std::shared_ptr<response> res)
+         [](const std::shared_ptr<request>& req,
+            const std::shared_ptr<response>& res)
          {
            req->run_task
              ([res](channel& channel)
diff --git a/examples/asio-sv.cc b/examples/asio-sv.cc
index d5c43c7f..0827c666 100644
--- a/examples/asio-sv.cc
+++ b/examples/asio-sv.cc
@@ -65,7 +65,8 @@ int main(int argc, char* argv[])
 
     server.listen
       ("*", port,
-       [](std::shared_ptr<request> req, std::shared_ptr<response> res)
+       [](const std::shared_ptr<request>& req,
+          const std::shared_ptr<response>& res)
        {
          res->write_head(200, { header{ "foo", "bar" } });
          res->end("hello, world");
diff --git a/examples/asio-sv2.cc b/examples/asio-sv2.cc
index 645e1d59..f173381b 100644
--- a/examples/asio-sv2.cc
+++ b/examples/asio-sv2.cc
@@ -69,7 +69,8 @@ int main(int argc, char* argv[])
 
     server.listen
       ("*", port,
-       [&docroot](std::shared_ptr<request> req, std::shared_ptr<response> res)
+       [&docroot](const std::shared_ptr<request>& req,
+                  const std::shared_ptr<response>& res)
        {
          auto path = percent_decode(req->path());
          if(!check_path(path)) {
diff --git a/examples/asio-sv3.cc b/examples/asio-sv3.cc
index a49ee3d8..241c6fea 100644
--- a/examples/asio-sv3.cc
+++ b/examples/asio-sv3.cc
@@ -69,7 +69,8 @@ int main(int argc, char* argv[])
 
     server.listen
       ("*", port,
-       [](std::shared_ptr<request> req, std::shared_ptr<response> res)
+       [](const std::shared_ptr<request>& req,
+          const std::shared_ptr<response>& res)
        {
          res->write_head(200);
 
diff --git a/src/asio_http2_impl.cc b/src/asio_http2_impl.cc
index 229dcf3b..23f3f1ce 100644
--- a/src/asio_http2_impl.cc
+++ b/src/asio_http2_impl.cc
@@ -204,7 +204,7 @@ std::string percent_decode(const std::string& s)
   return util::percentDecode(std::begin(s), std::end(s));
 }
 
-std::string http_date(time_t t)
+std::string http_date(int64_t t)
 {
   return util::http_date(t);
 }
diff --git a/src/includes/nghttp2/asio_http2.h b/src/includes/nghttp2/asio_http2.h
index aaca11da..f57eee76 100644
--- a/src/includes/nghttp2/asio_http2.h
+++ b/src/includes/nghttp2/asio_http2.h
@@ -180,8 +180,8 @@ private:
 
 // This is so called request callback.  Called every time request is
 // received.
-typedef std::function<void(std::shared_ptr<request>,
-                           std::shared_ptr<response>)> request_cb;
+typedef std::function<void(const std::shared_ptr<request>&,
+                           const std::shared_ptr<response>&)> request_cb;
 
 class http2_impl;
 
@@ -233,7 +233,7 @@ bool check_path(const std::string& path);
 std::string percent_decode(const std::string& s);
 
 // Returns HTTP date representation of current posix time |t|.
-std::string http_date(time_t t);
+std::string http_date(int64_t t);
 
 } // namespace asio_http2