diff --git a/examples/client.c b/examples/client.c
index 1fdbcdd6..1927e05a 100644
--- a/examples/client.c
+++ b/examples/client.c
@@ -152,7 +152,7 @@ static ssize_t send_callback(nghttp2_session *session _U_, const uint8_t *data,
   connection->want_io = IO_NONE;
   ERR_clear_error();
   rv = SSL_write(connection->ssl, data, (int)length);
-  if (rv < 0) {
+  if (rv <= 0) {
     int err = SSL_get_error(connection->ssl, rv);
     if (err == SSL_ERROR_WANT_WRITE || err == SSL_ERROR_WANT_READ) {
       connection->want_io =
@@ -529,8 +529,12 @@ static void fetch_uri(const struct URI *uri) {
   connection.want_io = IO_NONE;
 
   /* Send connection header in blocking I/O mode */
-  SSL_write(ssl, NGHTTP2_CLIENT_CONNECTION_PREFACE,
-            NGHTTP2_CLIENT_CONNECTION_PREFACE_LEN);
+  rv = SSL_write(ssl, NGHTTP2_CLIENT_CONNECTION_PREFACE,
+                 NGHTTP2_CLIENT_CONNECTION_PREFACE_LEN);
+  if (rv <= 0) {
+    dief("SSL_write failed: could not send connection preface",
+         ERR_error_string(ERR_get_error(), NULL));
+  }
 
   /* Here make file descriptor non-block */
   make_non_block(fd);
diff --git a/src/HttpServer.cc b/src/HttpServer.cc
index 8072905b..ca211c54 100644
--- a/src/HttpServer.cc
+++ b/src/HttpServer.cc
@@ -1470,7 +1470,7 @@ int start_listen(struct ev_loop *loop, Sessions *sessions,
       close(fd);
       continue;
     }
-    util::make_socket_nonblocking(fd);
+    (void)util::make_socket_nonblocking(fd);
 #ifdef IPV6_V6ONLY
     if (rp->ai_family == AF_INET6) {
       if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &val,
@@ -1547,7 +1547,10 @@ int HttpServer::run() {
     SSL_CTX_set_mode(ssl_ctx, SSL_MODE_AUTO_RETRY);
     SSL_CTX_set_mode(ssl_ctx, SSL_MODE_RELEASE_BUFFERS);
 
-    SSL_CTX_set_cipher_list(ssl_ctx, ssl::DEFAULT_CIPHER_LIST);
+    if (SSL_CTX_set_cipher_list(ssl_ctx, ssl::DEFAULT_CIPHER_LIST) == 0) {
+      std::cerr << ERR_error_string(ERR_get_error(), nullptr) << std::endl;
+      return -1;
+    }
 
     const unsigned char sid_ctx[] = "nghttpd";
     SSL_CTX_set_session_id_context(ssl_ctx, sid_ctx, sizeof(sid_ctx) - 1);