diff --git a/src/shrpx.cc b/src/shrpx.cc
index f561b583..677974da 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -2445,7 +2445,7 @@ int process_options(Config *config,
   auto &tlsconf = config->tls;
 
   if (tlsconf.npn_list.empty()) {
-    tlsconf.npn_list = util::parse_config_str_list(DEFAULT_NPN_LIST);
+    tlsconf.npn_list = util::split_str(DEFAULT_NPN_LIST, ',');
   }
   if (tlsconf.tls_proto_list.empty()) {
     tlsconf.tls_proto_list =
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index ae262557..066aa731 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -2305,7 +2305,7 @@ int parse_config(Config *config, int optid, const StringRef &opt,
     LOG(WARN) << opt << ": not implemented yet";
     return 0;
   case SHRPX_OPTID_NPN_LIST:
-    config->tls.npn_list = util::parse_config_str_list(optarg);
+    config->tls.npn_list = util::split_str(optarg, ',');
 
     return 0;
   case SHRPX_OPTID_TLS_PROTO_LIST:
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index 54f8275b..b3c98ed8 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -526,7 +526,7 @@ struct TLSConfig {
   std::vector<unsigned char> alpn_prefs;
   // list of supported NPN/ALPN protocol strings in the order of
   // preference.
-  std::vector<std::string> npn_list;
+  std::vector<StringRef> npn_list;
   // list of supported SSL/TLS protocol strings.
   std::vector<std::string> tls_proto_list;
   BIO_METHOD *bio_method;
diff --git a/src/shrpx_ssl.cc b/src/shrpx_ssl.cc
index 1e283e0d..a53dbe62 100644
--- a/src/shrpx_ssl.cc
+++ b/src/shrpx_ssl.cc
@@ -103,7 +103,7 @@ int verify_callback(int preverify_ok, X509_STORE_CTX *ctx) {
 } // namespace
 
 int set_alpn_prefs(std::vector<unsigned char> &out,
-                   const std::vector<std::string> &protos) {
+                   const std::vector<StringRef> &protos) {
   size_t len = 0;
 
   for (const auto &proto : protos) {
@@ -125,8 +125,7 @@ int set_alpn_prefs(std::vector<unsigned char> &out,
 
   for (const auto &proto : protos) {
     *ptr++ = proto.size();
-    memcpy(ptr, proto.c_str(), proto.size());
-    ptr += proto.size();
+    ptr = std::copy(std::begin(proto), std::end(proto), ptr);
   }
 
   return 0;
@@ -469,8 +468,7 @@ int alpn_select_proto_cb(SSL *ssl, const unsigned char **out,
       auto proto_len = *p;
 
       if (proto_id + proto_len <= end &&
-          util::streq(StringRef{target_proto_id},
-                      StringRef{proto_id, proto_len})) {
+          util::streq(target_proto_id, StringRef{proto_id, proto_len})) {
 
         *out = reinterpret_cast<const unsigned char *>(proto_id);
         *outlen = proto_len;
@@ -1320,10 +1318,10 @@ int cert_lookup_tree_add_cert_from_x509(CertLookupTree *lt, size_t idx,
   return 0;
 }
 
-bool in_proto_list(const std::vector<std::string> &protos,
+bool in_proto_list(const std::vector<StringRef> &protos,
                    const StringRef &needle) {
   for (auto &proto : protos) {
-    if (util::streq(StringRef{proto}, needle)) {
+    if (util::streq(proto, needle)) {
       return true;
     }
   }
diff --git a/src/shrpx_ssl.h b/src/shrpx_ssl.h
index b3952239..010072a6 100644
--- a/src/shrpx_ssl.h
+++ b/src/shrpx_ssl.h
@@ -167,7 +167,7 @@ int cert_lookup_tree_add_cert_from_x509(CertLookupTree *lt, size_t idx,
 
 // Returns true if |proto| is included in the
 // protocol list |protos|.
-bool in_proto_list(const std::vector<std::string> &protos,
+bool in_proto_list(const std::vector<StringRef> &protos,
                    const StringRef &proto);
 
 // Returns true if security requirement for HTTP/2 is fulfilled.
@@ -179,7 +179,7 @@ bool check_http2_requirement(SSL *ssl);
 long int create_tls_proto_mask(const std::vector<std::string> &tls_proto_list);
 
 int set_alpn_prefs(std::vector<unsigned char> &out,
-                   const std::vector<std::string> &protos);
+                   const std::vector<StringRef> &protos);
 
 // Setups server side SSL_CTX.  This function inspects get_config()
 // and if upstream_no_tls is true, returns nullptr.  Otherwise