diff --git a/include/http_data.h b/include/http_data.h
index 3db000d4..8588dfe5 100644
--- a/include/http_data.h
+++ b/include/http_data.h
@@ -41,6 +41,8 @@ struct http_res {
     std::string body;
     std::atomic<bool> final;
 
+    std::shared_mutex mres;
+
     std::atomic<bool> is_alive;
     std::atomic<void*> generator = nullptr;
 
diff --git a/include/http_server.h b/include/http_server.h
index 41554942..64a35627 100644
--- a/include/http_server.h
+++ b/include/http_server.h
@@ -109,6 +109,8 @@ public:
                     const bool destroy_after_use) :
             req(h_req), res(h_res), destroy_after_use(destroy_after_use), res_state(h_req->_req) {
 
+        std::shared_lock lk(res->mres);
+
         if(!res->is_alive || req->_req == nullptr || res->generator == nullptr) {
             return;
         }
diff --git a/src/http_server.cpp b/src/http_server.cpp
index 518d3175..8ddb7a72 100644
--- a/src/http_server.cpp
+++ b/src/http_server.cpp
@@ -261,11 +261,15 @@ void HttpServer::on_res_generator_dispose(void *self) {
     //LOG(INFO) << "on_res_generator_dispose fires";
     h2o_custom_generator_t* custom_generator = *static_cast<h2o_custom_generator_t**>(self);
 
-    custom_generator->res()->final = true;
-    custom_generator->res()->generator = nullptr;
-    custom_generator->res()->is_alive = false;
-    custom_generator->req()->notify();
-    custom_generator->res()->notify();
+    // locking to ensure dispose does not happen while the h2o req object is being written to
+    {
+        std::unique_lock lk(custom_generator->res()->mres);
+        custom_generator->res()->final = true;
+        custom_generator->res()->generator = nullptr;
+        custom_generator->res()->is_alive = false;
+        custom_generator->req()->notify();
+        custom_generator->res()->notify();
+    }
 
     delete custom_generator;
 }