diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 0682149f..24e89d05 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -1763,7 +1763,7 @@ int parse_config(const char *opt, const char *optarg,
 
     return 0;
   case SHRPX_OPTID_DH_PARAM_FILE:
-    mod_config()->tls.dh_param_file = strcopy(optarg);
+    mod_config()->tls.dh_param_file = optarg;
 
     return 0;
   case SHRPX_OPTID_SUBCERT: {
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index 3f5a8565..dbe8c9a5 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -429,7 +429,7 @@ struct TLSConfig {
   ImmutableString private_key_file;
   ImmutableString private_key_passwd;
   ImmutableString cert_file;
-  std::unique_ptr<char[]> dh_param_file;
+  ImmutableString dh_param_file;
   std::unique_ptr<char[]> ciphers;
   ImmutableString cacert;
   bool insecure;
diff --git a/src/shrpx_ssl.cc b/src/shrpx_ssl.cc
index f5d2b594..a7e00086 100644
--- a/src/shrpx_ssl.cc
+++ b/src/shrpx_ssl.cc
@@ -527,9 +527,9 @@ SSL_CTX *create_ssl_context(const char *private_key_file, const char *cert_file
 
 #endif // OPENSSL_NO_EC
 
-  if (tlsconf.dh_param_file) {
+  if (!tlsconf.dh_param_file.empty()) {
     // Read DH parameters from file
-    auto bio = BIO_new_file(tlsconf.dh_param_file.get(), "r");
+    auto bio = BIO_new_file(tlsconf.dh_param_file.c_str(), "r");
     if (bio == nullptr) {
       LOG(FATAL) << "BIO_new_file() failed: "
                  << ERR_error_string(ERR_get_error(), nullptr);