diff --git a/src/shrpx.cc b/src/shrpx.cc
index 17adf31d..71af4447 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -1986,8 +1986,8 @@ void process_options(
   {
     auto &dumpconf = http2conf.upstream.debug.dump;
 
-    if (dumpconf.request_header_file) {
-      auto path = dumpconf.request_header_file.get();
+    if (!dumpconf.request_header_file.empty()) {
+      auto path = dumpconf.request_header_file.c_str();
       auto f = open_file_for_write(path);
 
       if (f == nullptr) {
@@ -2007,8 +2007,8 @@ void process_options(
       }
     }
 
-    if (dumpconf.response_header_file) {
-      auto path = dumpconf.response_header_file.get();
+    if (!dumpconf.response_header_file.empty()) {
+      auto path = dumpconf.response_header_file.c_str();
       auto f = open_file_for_write(path);
 
       if (f == nullptr) {
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index d99ca91a..c16a6132 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -1919,13 +1919,11 @@ int parse_config(const char *opt, const char *optarg,
 
     return 0;
   case SHRPX_OPTID_FRONTEND_HTTP2_DUMP_REQUEST_HEADER:
-    mod_config()->http2.upstream.debug.dump.request_header_file =
-        strcopy(optarg);
+    mod_config()->http2.upstream.debug.dump.request_header_file = optarg;
 
     return 0;
   case SHRPX_OPTID_FRONTEND_HTTP2_DUMP_RESPONSE_HEADER:
-    mod_config()->http2.upstream.debug.dump.response_header_file =
-        strcopy(optarg);
+    mod_config()->http2.upstream.debug.dump.response_header_file = optarg;
 
     return 0;
   case SHRPX_OPTID_HTTP2_NO_COOKIE_CRUMBLING:
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index d8c63fd4..93d55ade 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -473,8 +473,8 @@ struct Http2Config {
   struct {
     struct {
       struct {
-        std::unique_ptr<char[]> request_header_file;
-        std::unique_ptr<char[]> response_header_file;
+        ImmutableString request_header_file;
+        ImmutableString response_header_file;
         FILE *request_header;
         FILE *response_header;
       } dump;