diff --git a/src/shrpx_client_handler.cc b/src/shrpx_client_handler.cc
index 0a1b55d6..7c9d4c23 100644
--- a/src/shrpx_client_handler.cc
+++ b/src/shrpx_client_handler.cc
@@ -46,7 +46,7 @@ namespace shrpx {
 namespace {
 void upstream_readcb(bufferevent *bev, void *arg)
 {
-  ClientHandler *handler = reinterpret_cast<ClientHandler*>(arg);
+  auto handler = reinterpret_cast<ClientHandler*>(arg);
   int rv = handler->on_read();
   if(rv != 0) {
     delete handler;
@@ -57,7 +57,7 @@ void upstream_readcb(bufferevent *bev, void *arg)
 namespace {
 void upstream_writecb(bufferevent *bev, void *arg)
 {
-  ClientHandler *handler = reinterpret_cast<ClientHandler*>(arg);
+  auto handler = reinterpret_cast<ClientHandler*>(arg);
   // We actually depend on write low-warter mark == 0.
   if(evbuffer_get_length(bufferevent_get_output(bev)) > 0) {
     // Possibly because of deferred callback, we may get this callback
@@ -67,7 +67,7 @@ void upstream_writecb(bufferevent *bev, void *arg)
   if(handler->get_should_close_after_write()) {
     delete handler;
   } else {
-    Upstream *upstream = handler->get_upstream();
+    auto upstream = handler->get_upstream();
     int rv = upstream->on_write();
     if(rv != 0) {
       delete handler;
@@ -79,7 +79,7 @@ void upstream_writecb(bufferevent *bev, void *arg)
 namespace {
 void upstream_eventcb(bufferevent *bev, short events, void *arg)
 {
-  ClientHandler *handler = reinterpret_cast<ClientHandler*>(arg);
+  auto handler = reinterpret_cast<ClientHandler*>(arg);
   bool finish = false;
   if(events & BEV_EVENT_EOF) {
     if(LOG_ENABLED(INFO)) {
@@ -252,9 +252,8 @@ ClientHandler::~ClientHandler()
   }
   shutdown(fd_, SHUT_WR);
   close(fd_);
-  for(std::set<DownstreamConnection*>::iterator i = dconn_pool_.begin();
-      i != dconn_pool_.end(); ++i) {
-    delete *i;
+  for(auto dconn : dconn_pool_) {
+    delete dconn;
   }
   if(LOG_ENABLED(INFO)) {
     CLOG(INFO, this) << "Deleted";
@@ -382,7 +381,7 @@ DownstreamConnection* ClientHandler::get_downstream_connection()
       return new HttpDownstreamConnection(this);
     }
   } else {
-    DownstreamConnection *dconn = *dconn_pool_.begin();
+    auto dconn = *std::begin(dconn_pool_);
     dconn_pool_.erase(dconn);
     if(LOG_ENABLED(INFO)) {
       CLOG(INFO, this) << "Reuse downstream connection DCONN:" << dconn
@@ -394,7 +393,7 @@ DownstreamConnection* ClientHandler::get_downstream_connection()
 
 size_t ClientHandler::get_pending_write_length()
 {
-  evbuffer *output = bufferevent_get_output(bev_);
+  auto output = bufferevent_get_output(bev_);
   return evbuffer_get_length(output);
 }
 
diff --git a/src/shrpx_downstream_connection.cc b/src/shrpx_downstream_connection.cc
index f33d9cac..0e09a7f6 100644
--- a/src/shrpx_downstream_connection.cc
+++ b/src/shrpx_downstream_connection.cc
@@ -31,7 +31,7 @@ namespace shrpx {
 
 DownstreamConnection::DownstreamConnection(ClientHandler *client_handler)
   : client_handler_(client_handler),
-    downstream_(0)
+    downstream_(nullptr)
 {}
 
 DownstreamConnection::~DownstreamConnection()
diff --git a/src/shrpx_downstream_queue.cc b/src/shrpx_downstream_queue.cc
index 52dea965..66a84de9 100644
--- a/src/shrpx_downstream_queue.cc
+++ b/src/shrpx_downstream_queue.cc
@@ -35,9 +35,8 @@ DownstreamQueue::DownstreamQueue()
 
 DownstreamQueue::~DownstreamQueue()
 {
-  for(std::map<int32_t, Downstream*>::iterator i = downstreams_.begin();
-      i != downstreams_.end(); ++i) {
-    delete (*i).second;
+  for(auto& kv : downstreams_) {
+    delete kv.second;
   }
 }
 
@@ -53,11 +52,11 @@ void DownstreamQueue::remove(Downstream *downstream)
 
 Downstream* DownstreamQueue::find(int32_t stream_id)
 {
-  std::map<int32_t, Downstream*>::iterator i = downstreams_.find(stream_id);
-  if(i == downstreams_.end()) {
-    return 0;
+  auto kv = downstreams_.find(stream_id);
+  if(kv == std::end(downstreams_)) {
+    return nullptr;
   } else {
-    return (*i).second;
+    return (*kv).second;
   }
 }
 
diff --git a/src/shrpx_http2_downstream_connection.cc b/src/shrpx_http2_downstream_connection.cc
index 6820030c..ce1f8b27 100644
--- a/src/shrpx_http2_downstream_connection.cc
+++ b/src/shrpx_http2_downstream_connection.cc
@@ -50,8 +50,8 @@ Http2DownstreamConnection::Http2DownstreamConnection
 (ClientHandler *client_handler)
   : DownstreamConnection(client_handler),
     http2session_(client_handler->get_http2_session()),
-    request_body_buf_(0),
-    sd_(0)
+    request_body_buf_(nullptr),
+    sd_(nullptr)
 {}
 
 Http2DownstreamConnection::~Http2DownstreamConnection()
@@ -71,7 +71,7 @@ Http2DownstreamConnection::~Http2DownstreamConnection()
   // Downstream and DownstreamConnection may be deleted
   // asynchronously.
   if(downstream_) {
-    downstream_->set_downstream_connection(0);
+    downstream_->set_downstream_connection(nullptr);
   }
   if(LOG_ENABLED(INFO)) {
     DCLOG(INFO, this) << "Deleted";
@@ -89,10 +89,10 @@ int Http2DownstreamConnection::init_request_body_buf()
     }
   } else {
     request_body_buf_ = evbuffer_new();
-    if(request_body_buf_ == 0) {
+    if(request_body_buf_ == nullptr) {
       return -1;
     }
-    evbuffer_setcb(request_body_buf_, 0, this);
+    evbuffer_setcb(request_body_buf_, nullptr, this);
   }
   return 0;
 }
@@ -122,8 +122,8 @@ void Http2DownstreamConnection::detach_downstream(Downstream *downstream)
   if(submit_rst_stream(downstream) == 0) {
     http2session_->notify();
   }
-  downstream->set_downstream_connection(0);
-  downstream_ = 0;
+  downstream->set_downstream_connection(nullptr);
+  downstream_ = nullptr;
 
   client_handler_->pool_downstream_connection(this);
 }
@@ -195,7 +195,7 @@ ssize_t http2_data_read_callback(nghttp2_session *session,
         }
         // Check dconn is still alive because Upstream::resume_read()
         // may delete downstream which will delete dconn.
-        if(sd->dconn == 0) {
+        if(sd->dconn == nullptr) {
           return NGHTTP2_ERR_DEFERRED;
         }
         if(evbuffer_get_length(body) == 0) {
@@ -498,12 +498,12 @@ void Http2DownstreamConnection::attach_stream_data(StreamData *sd)
 StreamData* Http2DownstreamConnection::detach_stream_data()
 {
   if(sd_) {
-    StreamData *sd = sd_;
-    sd_ = 0;
-    sd->dconn = 0;
+    auto sd = sd_;
+    sd_ = nullptr;
+    sd->dconn = nullptr;
     return sd;
   } else {
-    return 0;
+    return nullptr;
   }
 }