diff --git a/examples/shrpx_downstream.cc b/examples/shrpx_downstream.cc
index 5cf3bebe..78aa7f21 100644
--- a/examples/shrpx_downstream.cc
+++ b/examples/shrpx_downstream.cc
@@ -367,7 +367,11 @@ int Downstream::push_request_headers()
   }
   bufferevent *bev = dconn_->get_bev();
   evbuffer *output = bufferevent_get_output(bev);
-  evbuffer_add(output, hdrs.c_str(), hdrs.size());
+  int rv;
+  rv = evbuffer_add(output, hdrs.c_str(), hdrs.size());
+  if(rv != 0) {
+    return -1;
+  }
 
   dconn_->start_waiting_response();
   return 0;
@@ -392,17 +396,20 @@ int Downstream::push_upload_data_chunk(const uint8_t *data, size_t datalen)
     res += rv;
     rv = evbuffer_add(output, chunk_size_hex, rv);
     if(rv == -1) {
+      LOG(FATAL) << "evbuffer_add() failed";
       return -1;
     }
   }
   rv = evbuffer_add(output, data, datalen);
   if(rv == -1) {
+    LOG(FATAL) << "evbuffer_add() failed";
     return -1;
   }
   res += rv;
   if(chunked_request_) {
     rv = evbuffer_add(output, "\r\n", 2);
     if(rv == -1) {
+      LOG(FATAL) << "evbuffer_add() failed";
       return -1;
     }
     res += 2;
@@ -415,7 +422,10 @@ int Downstream::end_upload_data()
   if(chunked_request_) {
     bufferevent *bev = dconn_->get_bev();
     evbuffer *output = bufferevent_get_output(bev);
-    evbuffer_add(output, "0\r\n\r\n", 5);
+    if(evbuffer_add(output, "0\r\n\r\n", 5) != 0) {
+      LOG(FATAL) << "evbuffer_add() failed";
+      return -1;
+    }
   }
   return 0;
 }
diff --git a/examples/shrpx_https_upstream.cc b/examples/shrpx_https_upstream.cc
index 6e9e45ed..9e8062cf 100644
--- a/examples/shrpx_https_upstream.cc
+++ b/examples/shrpx_https_upstream.cc
@@ -159,7 +159,10 @@ int htp_hdrs_completecb(http_parser *htp)
     delete dconn;
     return -1;
   } else {
-    downstream->push_request_headers();
+    rv = downstream->push_request_headers();
+    if(rv != 0) {
+      return -1;
+    }
     downstream->set_request_state(Downstream::HEADER_COMPLETE);
     return 0;
   }
@@ -169,11 +172,15 @@ int htp_hdrs_completecb(http_parser *htp)
 namespace {
 int htp_bodycb(http_parser *htp, const char *data, size_t len)
 {
+  int rv;
   HttpsUpstream *upstream;
   upstream = reinterpret_cast<HttpsUpstream*>(htp->data);
   Downstream *downstream = upstream->get_last_downstream();
-  downstream->push_upload_data_chunk(reinterpret_cast<const uint8_t*>(data),
-                                     len);
+  rv = downstream->push_upload_data_chunk
+    (reinterpret_cast<const uint8_t*>(data), len);
+  if(rv != 0) {
+    return -1;
+  }
   return 0;
 }
 } // namespace
@@ -181,13 +188,17 @@ int htp_bodycb(http_parser *htp, const char *data, size_t len)
 namespace {
 int htp_msg_completecb(http_parser *htp)
 {
+  int rv;
   if(ENABLE_LOG) {
     LOG(INFO) << "Upstream https request complete";
   }
   HttpsUpstream *upstream;
   upstream = reinterpret_cast<HttpsUpstream*>(htp->data);
   Downstream *downstream = upstream->get_last_downstream();
-  downstream->end_upload_data();
+  rv = downstream->end_upload_data();
+  if(rv != 0) {
+    return -1;
+  }
   downstream->set_request_state(Downstream::MSG_COMPLETE);
   // Stop further processing to complete this request
   http_parser_pause(htp, 1);
diff --git a/examples/shrpx_spdy_upstream.cc b/examples/shrpx_spdy_upstream.cc
index f77d3c18..53fe838f 100644
--- a/examples/shrpx_spdy_upstream.cc
+++ b/examples/shrpx_spdy_upstream.cc
@@ -118,6 +118,9 @@ void on_stream_close_callback
         delete downstream;
       } else {
         // At this point, downstream read may be paused.
+
+        // If shrpx_downstream::push_request_headers() failed, the
+        // error is handled here.
         upstream->remove_downstream(downstream);
         delete downstream;
         // How to test this case? Request sufficient large download
@@ -201,7 +204,11 @@ void on_ctrl_recv_callback
       downstream->set_request_state(Downstream::CONNECT_FAIL);
       return;
     }
-    downstream->push_request_headers();
+    rv = downstream->push_request_headers();
+    if(rv != 0) {
+      upstream->rst_stream(downstream, SPDYLAY_INTERNAL_ERROR);
+      return;
+    }
     downstream->set_request_state(Downstream::HEADER_COMPLETE);
     if(frame->syn_stream.hd.flags & SPDYLAY_CTRL_FLAG_FIN) {
       if(ENABLE_LOG) {
@@ -228,7 +235,10 @@ void on_data_chunk_recv_callback(spdylay_session *session,
   SpdyUpstream *upstream = reinterpret_cast<SpdyUpstream*>(user_data);
   Downstream *downstream = upstream->find_downstream(stream_id);
   if(downstream) {
-    downstream->push_upload_data_chunk(data, len);
+    if(downstream->push_upload_data_chunk(data, len) != 0) {
+      upstream->rst_stream(downstream, SPDYLAY_INTERNAL_ERROR);
+      return;
+    }
     if(upstream->get_flow_control()) {
       downstream->inc_recv_window_size(len);
       if(downstream->get_recv_window_size() >