diff --git a/src/shrpx.cc b/src/shrpx.cc
index a53da086..19516c81 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -1088,7 +1088,8 @@ int main(int argc, char **argv)
   }
 
   if(!get_config()->npn_list) {
-    parse_config_npn_list(DEFAULT_NPN_LIST);
+    mod_config()->npn_list = parse_config_str_list(&mod_config()->npn_list_len,
+                                                   DEFAULT_NPN_LIST);
   }
 
   if(!get_config()->subcerts.empty()) {
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 902d6949..b60e02ac 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -221,15 +221,13 @@ void set_config_str(char **destp, const char *val)
   *destp = strdup(val);
 }
 
-int parse_config_npn_list(const char *s)
+char** parse_config_str_list(size_t *outlen, const char *s)
 {
-  delete [] mod_config()->npn_list;
   size_t len = 1;
   for(const char *first = s, *p = nullptr; (p = strchr(first, ','));
       ++len, first = p + 1);
   auto list = new char*[len];
-  auto t = strdup(s);
-  auto first = t;
+  auto first = strdup(s);
   len = 0;
   for(;;) {
     auto p = strchr(first, ',');
@@ -241,9 +239,8 @@ int parse_config_npn_list(const char *s)
     first = p + 1;
   }
   list[len++] = first;
-  mod_config()->npn_list = list;
-  mod_config()->npn_list_len = len;
-  return 0;
+  *outlen = len;
+  return list;
 }
 
 int parse_config(const char *opt, const char *optarg)
@@ -453,7 +450,9 @@ int parse_config(const char *opt, const char *optarg)
   } else if(util::strieq(opt, SHRPX_OPT_WRITE_BURST)) {
     mod_config()->write_burst = strtoul(optarg, nullptr, 10);
   } else if(util::strieq(opt, SHRPX_OPT_NPN_LIST)) {
-    parse_config_npn_list(optarg);
+    delete [] mod_config()->npn_list;
+    mod_config()->npn_list = parse_config_str_list(&mod_config()->npn_list_len,
+                                                   optarg);
   } else if(util::strieq(opt, SHRPX_OPT_VERIFY_CLIENT)) {
     mod_config()->verify_client = util::strieq(optarg, "yes");
   } else if(util::strieq(opt, SHRPX_OPT_VERIFY_CLIENT_CACERT)) {
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index 8d112e7b..6534a0db 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -226,13 +226,16 @@ int load_config(const char *filename);
 // Read passwd from |filename|
 std::string read_passwd_from_file(const char *filename);
 
-// Parses NPN protocol strings in |s| and stores the protocols list in
-// mod_config()->npn_list and assigns the number of elements in
-// mod_config()->npn_list_len. The |s| must be comma delimited list of
-// protocol strings. The strings must be delimited by a single command
-// and any white spaces around it are treated as a part of protocol
-// strings.  This function always succeeds and returns 0.
-int parse_config_npn_list(const char *s);
+// Parses comma delimited strings in |s| and returns the array of
+// pointers, each element points to the each substring in |s|. The
+// number of elements are stored in |*outlen|. The |s| must be comma
+// delimited list of strings. The strings must be delimited by a
+// single comma and any white spaces around it are treated as a part
+// of protocol strings. This function may modify |s| and the caller
+// must leave it as is after this call. This function allocates memory
+// to store the parsed strings and it is caller's responsibility to
+// deallocate the memory.
+char** parse_config_str_list(size_t *outlen, const char *s);
 
 // Copies NULL-terminated string |val| to |*destp|. If |*destp| is not
 // NULL, it is freed before copying.