diff --git a/src/shrpx.cc b/src/shrpx.cc
index 8d192acf..ccbdf6bf 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -2908,8 +2908,7 @@ int process_options(Config *config,
     auto iov = make_byte_ref(config->balloc, SHRPX_OBFUSCATED_NODE_LENGTH + 2);
     auto p = iov.base;
     *p++ = '_';
-    std::random_device rd;
-    auto gen = util::make_mt19937(rd);
+    auto gen = util::make_mt19937();
     p = util::random_alpha_digit(p, p + SHRPX_OBFUSCATED_NODE_LENGTH, gen);
     *p = '\0';
     fwdconf.by_obfuscated = StringRef{iov.base, p};
diff --git a/src/shrpx_connection_handler.cc b/src/shrpx_connection_handler.cc
index 29d67ca0..0de4e4c3 100644
--- a/src/shrpx_connection_handler.cc
+++ b/src/shrpx_connection_handler.cc
@@ -232,11 +232,9 @@ int ConnectionHandler::create_single_worker() {
     all_ssl_ctx_.push_back(session_cache_ssl_ctx);
   }
 
-  std::random_device rd;
-
   single_worker_ = make_unique<Worker>(
       loop_, sv_ssl_ctx, cl_ssl_ctx, session_cache_ssl_ctx, cert_tree_.get(),
-      ticket_keys_, this, config->conn.downstream, util::make_mt19937(rd));
+      ticket_keys_, this, config->conn.downstream);
 #ifdef HAVE_MRUBY
   if (single_worker_->create_mruby_context() != 0) {
     return -1;
@@ -278,8 +276,6 @@ int ConnectionHandler::create_worker_thread(size_t num) {
     ++num;
   }
 
-  std::random_device rd;
-
   for (size_t i = 0; i < num; ++i) {
     auto loop = ev_loop_new(config->ev_loop_flags);
 
@@ -295,7 +291,7 @@ int ConnectionHandler::create_worker_thread(size_t num) {
     }
     auto worker = make_unique<Worker>(
         loop, sv_ssl_ctx, cl_ssl_ctx, session_cache_ssl_ctx, cert_tree_.get(),
-        ticket_keys_, this, config->conn.downstream, util::make_mt19937(rd));
+        ticket_keys_, this, config->conn.downstream);
 #ifdef HAVE_MRUBY
     if (worker->create_mruby_context() != 0) {
       return -1;
diff --git a/src/shrpx_worker.cc b/src/shrpx_worker.cc
index 74b30c5a..87ae96e4 100644
--- a/src/shrpx_worker.cc
+++ b/src/shrpx_worker.cc
@@ -114,9 +114,8 @@ Worker::Worker(struct ev_loop *loop, SSL_CTX *sv_ssl_ctx, SSL_CTX *cl_ssl_ctx,
                ssl::CertLookupTree *cert_tree,
                const std::shared_ptr<TicketKeys> &ticket_keys,
                ConnectionHandler *conn_handler,
-               std::shared_ptr<DownstreamConfig> downstreamconf,
-               std::mt19937 randgen)
-    : randgen_(std::move(randgen)),
+               std::shared_ptr<DownstreamConfig> downstreamconf)
+    : randgen_(util::make_mt19937()),
       worker_stat_{},
       dns_tracker_(loop),
       loop_(loop),
diff --git a/src/shrpx_worker.h b/src/shrpx_worker.h
index 8c94cdc2..9b77eb5b 100644
--- a/src/shrpx_worker.h
+++ b/src/shrpx_worker.h
@@ -223,8 +223,7 @@ public:
          ssl::CertLookupTree *cert_tree,
          const std::shared_ptr<TicketKeys> &ticket_keys,
          ConnectionHandler *conn_handler,
-         std::shared_ptr<DownstreamConfig> downstreamconf,
-         std::mt19937 randgen);
+         std::shared_ptr<DownstreamConfig> downstreamconf);
   ~Worker();
   void run_async();
   void wait();
diff --git a/src/shrpx_worker_process.cc b/src/shrpx_worker_process.cc
index 2e1aa708..aa335318 100644
--- a/src/shrpx_worker_process.cc
+++ b/src/shrpx_worker_process.cc
@@ -412,8 +412,7 @@ int worker_process_event_loop(WorkerProcessConfig *wpconf) {
 
   auto loop = EV_DEFAULT;
 
-  std::random_device rd;
-  auto gen = util::make_mt19937(rd);
+  auto gen = util::make_mt19937();
 
   ConnectionHandler conn_handler(loop, gen);
 
diff --git a/src/util.cc b/src/util.cc
index e31af042..0adb6727 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -1452,7 +1452,10 @@ StringRef extract_host(const StringRef &hostport) {
   return StringRef{std::begin(hostport), p};
 }
 
-std::mt19937 make_mt19937(std::random_device &rd) { return std::mt19937(rd()); }
+std::mt19937 make_mt19937() {
+  std::random_device rd;
+  return std::mt19937(rd());
+}
 
 } // namespace util
 
diff --git a/src/util.h b/src/util.h
index 123fd5df..49d0c4b1 100644
--- a/src/util.h
+++ b/src/util.h
@@ -744,8 +744,8 @@ int sha256(uint8_t *buf, const StringRef &s);
 // NULL-terminated.
 StringRef extract_host(const StringRef &hostport);
 
-// Returns new std::mt19937 object, seeded by |rd|.
-std::mt19937 make_mt19937(std::random_device &rd);
+// Returns new std::mt19937 object.
+std::mt19937 make_mt19937();
 
 } // namespace util