diff --git a/src/shrpx_connect_blocker.h b/src/shrpx_connect_blocker.h
index 625422f1..1d845921 100644
--- a/src/shrpx_connect_blocker.h
+++ b/src/shrpx_connect_blocker.h
@@ -66,7 +66,7 @@ public:
   void call_unblock_func();
 
 private:
-  std::mt19937 gen_;
+  std::mt19937 &gen_;
   // Called when blocking is started
   std::function<void()> block_func_;
   // Called when unblocked