diff --git a/lib/includes/nghttp2/nghttp2.h b/lib/includes/nghttp2/nghttp2.h
index 6e5e1bf8..80334d27 100644
--- a/lib/includes/nghttp2/nghttp2.h
+++ b/lib/includes/nghttp2/nghttp2.h
@@ -49,6 +49,24 @@ extern "C" {
  */
 #define NGHTTP2_PROTO_VERSION_ID_LEN 5
 
+/**
+ * @macro
+ *
+ * The seriazlied form of ALPN protocol identifier this library
+ * supports.  Notice that first byte is the length of following
+ * protocol identifier.  This is the same wire format of `TLS ALPN
+ * extension <https://tools.ietf.org/html/rfc7301>`_.  This is useful
+ * to process incoming ALPN tokens in wire format.
+ */
+#define NGHTTP2_PROTO_ALPN "\x5h2-14"
+
+/**
+ * @macro
+ *
+ * The length of :macro:`NGHTTP2_PROTO_ALPN`.
+ */
+#define NGHTTP2_PROTO_ALPN_LEN (sizeof(NGHTTP2_PROTO_ALPN) - 1)
+
 /**
  * @macro
  *
diff --git a/lib/nghttp2_npn.c b/lib/nghttp2_npn.c
index e4978357..a8bdb237 100644
--- a/lib/nghttp2_npn.c
+++ b/lib/nghttp2_npn.c
@@ -26,29 +26,32 @@
 
 #include <string.h>
 
+static int select_next_protocol(unsigned char **out, unsigned char *outlen,
+                                const unsigned char *in, unsigned int inlen,
+                                const char *key, unsigned int keylen) {
+  unsigned int i;
+  for (i = 0; i + keylen <= inlen; i += in [i] + 1) {
+    if (memcmp(&in[i], key, keylen) == 0) {
+      *out = (unsigned char *)&in[i + 1];
+      *outlen = in[i];
+      return 0;
+    }
+  }
+  return -1;
+}
+
+#define NGHTTP2_HTTP_1_1_ALPN "\x8http/1.1"
+#define NGHTTP2_HTTP_1_1_ALPN_LEN (sizeof(NGHTTP2_HTTP_1_1_ALPN) - 1)
+
 int nghttp2_select_next_protocol(unsigned char **out, unsigned char *outlen,
                                  const unsigned char *in, unsigned int inlen) {
-  int http_selected = 0;
-  unsigned int i = 0;
-  for (; i < inlen; i += in [i] + 1) {
-    if (in[i] == NGHTTP2_PROTO_VERSION_ID_LEN && i + 1 + in[i] <= inlen &&
-        memcmp(&in[i + 1], NGHTTP2_PROTO_VERSION_ID, in[i]) == 0) {
-      *out = (unsigned char *)&in[i + 1];
-      *outlen = in[i];
-      return 1;
-    }
-    if (in[i] == 8 && i + 1 + in[i] <= inlen &&
-        memcmp(&in[i + 1], "http/1.1", in[i]) == 0) {
-      http_selected = 1;
-      *out = (unsigned char *)&in[i + 1];
-      *outlen = in[i];
-      /* Go through to the next iteration, because "HTTP/2" may be
-         there */
-    }
+  if (select_next_protocol(out, outlen, in, inlen, NGHTTP2_PROTO_ALPN,
+                           NGHTTP2_PROTO_ALPN_LEN) == 0) {
+    return 1;
   }
-  if (http_selected) {
+  if (select_next_protocol(out, outlen, in, inlen, NGHTTP2_HTTP_1_1_ALPN,
+                           NGHTTP2_HTTP_1_1_ALPN_LEN) == 0) {
     return 0;
-  } else {
-    return -1;
   }
+  return -1;
 }
diff --git a/src/util.cc b/src/util.cc
index f8f255fa..9bcf1d3a 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -47,9 +47,6 @@
 
 namespace nghttp2 {
 
-const unsigned char NGHTTP2_H2_PROTO_ALIAS[] = "h2-16";
-size_t NGHTTP2_H2_PROTO_ALIAS_LEN = sizeof(NGHTTP2_H2_PROTO_ALIAS) - 1;
-
 namespace util {
 
 const char DEFAULT_STRIP_CHARSET[] = "\r\n\t ";
@@ -786,28 +783,19 @@ int64_t to_time64(const timeval &tv) {
 bool check_h2_is_selected(const unsigned char *proto, size_t len) {
   return streq(NGHTTP2_PROTO_VERSION_ID, NGHTTP2_PROTO_VERSION_ID_LEN, proto,
                len) ||
-         streq(NGHTTP2_H2_PROTO_ALIAS, NGHTTP2_H2_PROTO_ALIAS_LEN, proto, len);
+         streq(NGHTTP2_H2_16_ID, NGHTTP2_H2_16_ID_LEN, proto, len);
 }
 
 namespace {
 bool select_h2(const unsigned char **out, unsigned char *outlen,
-               const unsigned char *in, unsigned int inlen,
-               const unsigned char *target, unsigned int tlen) {
-  for (auto p = in, end = in + inlen; p < end;) {
-    auto len = *p++;
-    if (p + len > end) {
-      return false;
-    }
-    if (len != tlen) {
-      p += len;
-      continue;
-    }
-    if (memcmp(target, p, tlen) == 0) {
-      *out = target;
-      *outlen = tlen;
+               const unsigned char *in, unsigned int inlen, const char *key,
+               unsigned int keylen) {
+  for (auto p = in, end = in + inlen; p + keylen <= end; p += *p + 1) {
+    if (memcmp(key, p, keylen) == 0) {
+      *out = p + 1;
+      *outlen = *p;
       return true;
     }
-    p += len;
   }
   return false;
 }
@@ -815,24 +803,19 @@ bool select_h2(const unsigned char **out, unsigned char *outlen,
 
 bool select_h2(const unsigned char **out, unsigned char *outlen,
                const unsigned char *in, unsigned int inlen) {
-  return select_h2(out, outlen, in, inlen, NGHTTP2_H2_PROTO_ALIAS,
-                   NGHTTP2_H2_PROTO_ALIAS_LEN) ||
-         select_h2(
-             out, outlen, in, inlen,
-             reinterpret_cast<const unsigned char *>(NGHTTP2_PROTO_VERSION_ID),
-             NGHTTP2_PROTO_VERSION_ID_LEN);
+  return select_h2(out, outlen, in, inlen, NGHTTP2_H2_16_ALPN,
+                   NGHTTP2_H2_16_ALPN_LEN) ||
+         select_h2(out, outlen, in, inlen, NGHTTP2_PROTO_ALPN,
+                   NGHTTP2_PROTO_ALPN_LEN);
 }
 
 std::vector<unsigned char> get_default_alpn() {
-  auto res = std::vector<unsigned char>(1 + NGHTTP2_PROTO_VERSION_ID_LEN + 1 +
-                                        NGHTTP2_H2_PROTO_ALIAS_LEN);
-  auto p = res.data();
+  auto res = std::vector<unsigned char>(NGHTTP2_PROTO_ALPN_LEN +
+                                        NGHTTP2_H2_16_ALPN_LEN);
+  auto p = std::begin(res);
 
-  *p++ = NGHTTP2_H2_PROTO_ALIAS_LEN;
-  memcpy(p, NGHTTP2_H2_PROTO_ALIAS, NGHTTP2_H2_PROTO_ALIAS_LEN);
-  p += NGHTTP2_H2_PROTO_ALIAS_LEN;
-  *p++ = NGHTTP2_PROTO_VERSION_ID_LEN;
-  memcpy(p, NGHTTP2_PROTO_VERSION_ID, NGHTTP2_PROTO_VERSION_ID_LEN);
+  p = std::copy_n(NGHTTP2_H2_16_ALPN, NGHTTP2_H2_16_ALPN_LEN, p);
+  p = std::copy_n(NGHTTP2_PROTO_ALPN, NGHTTP2_PROTO_ALPN_LEN, p);
 
   return res;
 }
diff --git a/src/util.h b/src/util.h
index 186f7673..7b233b8c 100644
--- a/src/util.h
+++ b/src/util.h
@@ -44,11 +44,13 @@
 
 namespace nghttp2 {
 
-// The additional HTTP/2 protocol ALPN ID we also supports for our
-// applications.  This will be removed once HTTP/2 specification is
-// finalized.
-extern const unsigned char NGHTTP2_H2_PROTO_ALIAS[];
-extern size_t NGHTTP2_H2_PROTO_ALIAS_LEN;
+// The additional HTTP/2 protocol ALPN protocol identifier we also
+// supports for our applications.  This will be removed once HTTP/2
+// specification is finalized.
+#define NGHTTP2_H2_16_ALPN "\x5h2-16"
+#define NGHTTP2_H2_16_ALPN_LEN (sizeof(NGHTTP2_H2_16_ALPN) - 1)
+#define NGHTTP2_H2_16_ID "h2-16"
+#define NGHTTP2_H2_16_ID_LEN (sizeof(NGHTTP2_H2_16_ID) - 1)
 
 namespace util {
 
diff --git a/src/util_test.cc b/src/util_test.cc
index 05e5dba9..f0871d69 100644
--- a/src/util_test.cc
+++ b/src/util_test.cc
@@ -160,9 +160,8 @@ void test_util_select_h2(void) {
   // picked up because it has precedence over the other.
   const unsigned char t6[] = "\x5h2-14\x5h2-16";
   CU_ASSERT(util::select_h2(&out, &outlen, t6, sizeof(t6) - 1));
-  CU_ASSERT(memcmp(NGHTTP2_H2_PROTO_ALIAS, out, NGHTTP2_H2_PROTO_ALIAS_LEN) ==
-            0);
-  CU_ASSERT(NGHTTP2_H2_PROTO_ALIAS_LEN == outlen);
+  CU_ASSERT(memcmp(NGHTTP2_H2_16_ID, out, NGHTTP2_H2_16_ID_LEN) == 0);
+  CU_ASSERT(NGHTTP2_H2_16_ID_LEN == outlen);
 }
 
 void test_util_ipv6_numeric_addr(void) {