core/modules/big_pipe/src/Render/BigPipeResponse.php | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/core/modules/big_pipe/src/Render/BigPipeResponse.php b/core/modules/big_pipe/src/Render/BigPipeResponse.php
index ba4d5f0..328a709 100644
--- a/core/modules/big_pipe/src/Render/BigPipeResponse.php
+++ b/core/modules/big_pipe/src/Render/BigPipeResponse.php
@@ -72,6 +72,11 @@ protected function populateBasedOnOriginalHtmlResponse() {
       ->setAttachments($this->originalHtmlResponse->getAttachments())
       ->addCacheableDependency($this->originalHtmlResponse->getCacheableMetadata());
 
+    // A BigPipe response can never be cached, because it is intended for a
+    // single user.
+    // @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.1
+    $this->setPrivate();
+
     // Inform surrogates how they should handle BigPipe responses:
     // - "no-store" specifies that the response should not be stored in cache;
     //   it is only to be used for the original request