diff --git a/src/shrpx_http2_upstream.cc b/src/shrpx_http2_upstream.cc
index 31cf8cac..d67cf03d 100644
--- a/src/shrpx_http2_upstream.cc
+++ b/src/shrpx_http2_upstream.cc
@@ -46,8 +46,8 @@ using namespace nghttp2;
 namespace shrpx {
 
 namespace {
-const size_t OUTBUF_MAX_THRES = 64*1024;
-const size_t INBUF_MAX_THRES = 64*1024;
+const size_t OUTBUF_MAX_THRES = 16*1024;
+const size_t INBUF_MAX_THRES = 16*1024;
 } // namespace
 
 namespace {
diff --git a/src/shrpx_https_upstream.cc b/src/shrpx_https_upstream.cc
index dff44a38..ac6a1bed 100644
--- a/src/shrpx_https_upstream.cc
+++ b/src/shrpx_https_upstream.cc
@@ -44,7 +44,7 @@ using namespace nghttp2;
 namespace shrpx {
 
 namespace {
-const size_t OUTBUF_MAX_THRES = 64*1024;
+const size_t OUTBUF_MAX_THRES = 16*1024;
 } // namespace
 
 HttpsUpstream::HttpsUpstream(ClientHandler *handler)
diff --git a/src/shrpx_spdy_upstream.cc b/src/shrpx_spdy_upstream.cc
index 8cf6c763..53fdb5f6 100644
--- a/src/shrpx_spdy_upstream.cc
+++ b/src/shrpx_spdy_upstream.cc
@@ -45,8 +45,8 @@ using namespace nghttp2;
 namespace shrpx {
 
 namespace {
-const size_t OUTBUF_MAX_THRES = 64*1024;
-const size_t INBUF_MAX_THRES = 64*1024;
+const size_t OUTBUF_MAX_THRES = 16*1024;
+const size_t INBUF_MAX_THRES = 16*1024;
 } // namespace
 
 namespace {