diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 1e023d18..4d95ffe2 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -2205,7 +2205,7 @@ int parse_config(const char *opt, const char *optarg,
 
   case SHRPX_OPTID_MRUBY_FILE:
 #ifdef HAVE_MRUBY
-    mod_config()->mruby_file = strcopy(optarg);
+    mod_config()->mruby_file = optarg;
 #else  // !HAVE_MRUBY
     LOG(WARN) << opt
               << ": ignored because mruby support is disabled at build time.";
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index 03b3700b..80f0e06e 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -584,7 +584,7 @@ struct Config {
   ImmutableString pid_file;
   ImmutableString conf_path;
   ImmutableString user;
-  std::unique_ptr<char[]> mruby_file;
+  ImmutableString mruby_file;
   char **original_argv;
   char **argv;
   char *cwd;
diff --git a/src/shrpx_mruby.cc b/src/shrpx_mruby.cc
index 5b1b3967..bd57c146 100644
--- a/src/shrpx_mruby.cc
+++ b/src/shrpx_mruby.cc
@@ -31,7 +31,6 @@
 #include "shrpx_config.h"
 #include "shrpx_mruby_module.h"
 #include "shrpx_downstream_connection.h"
-#include "template.h"
 
 namespace shrpx {
 
@@ -146,12 +145,12 @@ mrb_value instantiate_app(mrb_state *mrb, RProc *proc) {
 // very hard to write these kind of code because mruby has almost no
 // documentation aobut compiling or generating code, at least at the
 // time of this writing.
-RProc *compile(mrb_state *mrb, const char *filename) {
-  if (filename == nullptr) {
+RProc *compile(mrb_state *mrb, const StringRef &filename) {
+  if (filename.empty()) {
     return nullptr;
   }
 
-  auto infile = fopen(filename, "rb");
+  auto infile = fopen(filename.c_str(), "rb");
   if (infile == nullptr) {
     return nullptr;
   }
@@ -185,8 +184,8 @@ RProc *compile(mrb_state *mrb, const char *filename) {
   return proc;
 }
 
-std::unique_ptr<MRubyContext> create_mruby_context(const char *filename) {
-  if (!filename) {
+std::unique_ptr<MRubyContext> create_mruby_context(const StringRef &filename) {
+  if (filename.empty()) {
     return make_unique<MRubyContext>(nullptr, mrb_nil_value(), mrb_nil_value());
   }
 
diff --git a/src/shrpx_mruby.h b/src/shrpx_mruby.h
index 95f0430c..55a18351 100644
--- a/src/shrpx_mruby.h
+++ b/src/shrpx_mruby.h
@@ -32,6 +32,8 @@
 #include <mruby.h>
 #include <mruby/proc.h>
 
+#include "template.h"
+
 using namespace nghttp2;
 
 namespace shrpx {
@@ -69,9 +71,9 @@ struct MRubyAssocData {
   bool response_headers_dirty;
 };
 
-RProc *compile(mrb_state *mrb, const char *filename);
+RProc *compile(mrb_state *mrb, const StringRef &filename);
 
-std::unique_ptr<MRubyContext> create_mruby_context(const char *filename);
+std::unique_ptr<MRubyContext> create_mruby_context(const StringRef &filename);
 
 // Return interned |ptr|.
 mrb_sym intern_ptr(mrb_state *mrb, void *ptr);
diff --git a/src/shrpx_worker.cc b/src/shrpx_worker.cc
index 83cfff9b..604f9058 100644
--- a/src/shrpx_worker.cc
+++ b/src/shrpx_worker.cc
@@ -290,8 +290,7 @@ std::mt19937 &Worker::get_randgen() { return randgen_; }
 
 #ifdef HAVE_MRUBY
 int Worker::create_mruby_context() {
-  auto mruby_file = get_config()->mruby_file.get();
-  mruby_ctx_ = mruby::create_mruby_context(mruby_file);
+  mruby_ctx_ = mruby::create_mruby_context(StringRef{get_config()->mruby_file});
   if (!mruby_ctx_) {
     return -1;
   }