diff --git a/lib/nghttp2_hd.c b/lib/nghttp2_hd.c
index a73e8c7e..86773b7e 100644
--- a/lib/nghttp2_hd.c
+++ b/lib/nghttp2_hd.c
@@ -999,7 +999,7 @@ static int deflate_nv(nghttp2_hd_deflater *deflater,
 {
   int rv;
   search_result res;
-  ssize_t idx = -1;
+  ssize_t idx;
   int incidx = 0;
   uint32_t name_hash = hash(nv->name, nv->namelen);
   uint32_t value_hash = hash(nv->value, nv->valuelen);
diff --git a/lib/nghttp2_session.c b/lib/nghttp2_session.c
index 22a73b09..9c135f58 100644
--- a/lib/nghttp2_session.c
+++ b/lib/nghttp2_session.c
@@ -1511,7 +1511,7 @@ static int session_headers_add_pad(nghttp2_session *session,
   padlen = padded_payloadlen - frame->hd.length;
 
   DEBUGF(fprintf(stderr,
-                 "send: padding selected: payloadlen=%zu, padlen=%zu\n",
+                 "send: padding selected: payloadlen=%zd, padlen=%zu\n",
                  padded_payloadlen, padlen));
 
   rv = nghttp2_frame_add_pad(framebufs, &frame->hd, padlen);
@@ -1784,9 +1784,9 @@ static int session_prep_frame(nghttp2_session *session,
 
     rv = nghttp2_session_predicate_data_send(session, frame->hd.stream_id);
     if(rv != 0) {
-      int rv2;
-
       if(stream) {
+        int rv2;
+
         rv2 = nghttp2_stream_detach_data(stream, &session->ob_da_pq,
                                          session->last_cycle);
 
@@ -5389,7 +5389,7 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session,
           }
         }
 
-        DEBUGF(fprintf(stderr, "recv: data_readlen=%zu\n", data_readlen));
+        DEBUGF(fprintf(stderr, "recv: data_readlen=%zd\n", data_readlen));
 
         if(stream && data_readlen > 0 &&
            session->callbacks.on_data_chunk_recv_callback) {
@@ -5815,7 +5815,7 @@ int nghttp2_session_pack_data(nghttp2_session *session,
            use safe limit. */
         payloadlen = datamax;
 
-        DEBUGF(fprintf(stderr, "send: use safe limit payloadlen=%zu",
+        DEBUGF(fprintf(stderr, "send: use safe limit payloadlen=%zd",
                        payloadlen));
       } else {
         assert(&session->aob.framebufs == bufs);
diff --git a/src/HttpServer.cc b/src/HttpServer.cc
index 01f97a3e..f5ca5af0 100644
--- a/src/HttpServer.cc
+++ b/src/HttpServer.cc
@@ -674,7 +674,6 @@ int Http2Handler::submit_non_final_response(const std::string& status,
 int Http2Handler::submit_push_promise(Stream *stream,
                                       const std::string& push_path)
 {
-  std::string authority;
   auto itr = std::lower_bound(std::begin(stream->headers),
                               std::end(stream->headers),
                               Header(":authority", ""));
diff --git a/src/deflatehd.cc b/src/deflatehd.cc
index 7a5b6d78..1e7f3c3a 100644
--- a/src/deflatehd.cc
+++ b/src/deflatehd.cc
@@ -79,7 +79,7 @@ static void to_hex(char *dest, const uint8_t *src, size_t len)
 
 static void output_to_json(nghttp2_hd_deflater *deflater,
                            nghttp2_bufs *bufs, size_t inputlen,
-                           const std::vector<nghttp2_nv> nva,
+                           const std::vector<nghttp2_nv>& nva,
                            int seq)
 {
   auto len = nghttp2_bufs_len(bufs);
diff --git a/src/nghttp.cc b/src/nghttp.cc
index 28097145..aa053765 100644
--- a/src/nghttp.cc
+++ b/src/nghttp.cc
@@ -1122,8 +1122,8 @@ int on_data_chunk_recv_callback
  const uint8_t *data, size_t len, void *user_data)
 {
   auto client = get_session(user_data);
-  auto req =
-    (Request*)nghttp2_session_get_stream_user_data(session, stream_id);
+  auto req = static_cast<Request*>
+    (nghttp2_session_get_stream_user_data(session, stream_id));
 
   if(!req) {
     return 0;
@@ -1301,8 +1301,8 @@ int on_header_callback(nghttp2_session *session,
 
   switch(frame->hd.type) {
   case NGHTTP2_HEADERS: {
-    auto req = (Request*)nghttp2_session_get_stream_user_data
-      (session, frame->hd.stream_id);
+    auto req = static_cast<Request*>
+      (nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
 
     if(!req) {
       break;
@@ -1330,8 +1330,9 @@ int on_header_callback(nghttp2_session *session,
     break;
   }
   case NGHTTP2_PUSH_PROMISE: {
-    auto req = (Request*)nghttp2_session_get_stream_user_data
-      (session, frame->push_promise.promised_stream_id);
+    auto req = static_cast<Request*>
+      (nghttp2_session_get_stream_user_data
+       (session, frame->push_promise.promised_stream_id));
 
     if(!req) {
       break;
@@ -1369,8 +1370,8 @@ int on_frame_recv_callback2
   auto client = get_session(user_data);
   switch(frame->hd.type) {
   case NGHTTP2_HEADERS: {
-    auto req = (Request*)nghttp2_session_get_stream_user_data
-      (session, frame->hd.stream_id);
+    auto req = static_cast<Request*>
+      (nghttp2_session_get_stream_user_data(session, frame->hd.stream_id));
     // If this is the HTTP Upgrade with OPTIONS method to avoid POST,
     // req is nullptr.
     if(!req) {
@@ -1414,8 +1415,9 @@ int on_frame_recv_callback2
     }
     break;
   case NGHTTP2_PUSH_PROMISE: {
-    auto req = (Request*)nghttp2_session_get_stream_user_data
-      (session, frame->push_promise.promised_stream_id);
+    auto req = static_cast<Request*>
+      (nghttp2_session_get_stream_user_data
+       (session, frame->push_promise.promised_stream_id));
     if(!req) {
       break;
     }
@@ -1472,8 +1474,8 @@ int on_stream_close_callback
  void *user_data)
 {
   auto client = get_session(user_data);
-  auto req =
-    (Request*)nghttp2_session_get_stream_user_data(session, stream_id);
+  auto req = static_cast<Request*>
+    (nghttp2_session_get_stream_user_data(session, stream_id));
 
   if(!req) {
     return 0;
@@ -1798,8 +1800,8 @@ ssize_t file_read_callback
  uint8_t *buf, size_t length, uint32_t *data_flags,
  nghttp2_data_source *source, void *user_data)
 {
-  auto req = (Request*)nghttp2_session_get_stream_user_data
-    (session, stream_id);
+  auto req = static_cast<Request*>
+    (nghttp2_session_get_stream_user_data(session, stream_id));
   assert(req);
   int fd = source->fd;
   ssize_t nread;