core/lib/Drupal/Core/Render/PlaceholderingRenderCache.php        | 5 +++++
 core/modules/big_pipe/src/Render/Placeholder/BigPipeStrategy.php | 9 ++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/core/lib/Drupal/Core/Render/PlaceholderingRenderCache.php b/core/lib/Drupal/Core/Render/PlaceholderingRenderCache.php
index 98b58fc..8b71048 100644
--- a/core/lib/Drupal/Core/Render/PlaceholderingRenderCache.php
+++ b/core/lib/Drupal/Core/Render/PlaceholderingRenderCache.php
@@ -92,6 +92,11 @@ public function __construct(RequestStack $request_stack, CacheFactoryInterface $
    * {@inheritdoc}
    */
   public function get(array $elements) {
+    // @todo remove this check when https://www.drupal.org/node/2367555 lands.
+    if (!$this->requestStack->getCurrentRequest()->isMethodSafe()) {
+      return FALSE;
+    }
+
     // When rendering placeholders, special case auto-placeholdered elements:
     // avoid retrieving them from cache again, or rendering them again.
     if (isset($elements['#create_placeholder']) && $elements['#create_placeholder'] === FALSE) {
diff --git a/core/modules/big_pipe/src/Render/Placeholder/BigPipeStrategy.php b/core/modules/big_pipe/src/Render/Placeholder/BigPipeStrategy.php
index 0edf3ba..ae5cf1c 100644
--- a/core/modules/big_pipe/src/Render/Placeholder/BigPipeStrategy.php
+++ b/core/modules/big_pipe/src/Render/Placeholder/BigPipeStrategy.php
@@ -105,12 +105,19 @@ public function __construct(SessionConfigurationInterface $session_configuration
    * {@inheritdoc}
    */
   public function processPlaceholders(array $placeholders) {
+    $request = $this->requestStack->getCurrentRequest();
+
+    // @todo remove this check when https://www.drupal.org/node/2367555 lands.
+    if (!$request->isMethodSafe()) {
+      return [];
+    }
+
     // Routes can opt out from using the BigPipe HTML delivery technique.
     if ($this->routeMatch->getRouteObject()->getOption('_no_big_pipe')) {
       return [];
     }
 
-    if (!$this->sessionConfiguration->hasSession($this->requestStack->getCurrentRequest())) {
+    if (!$this->sessionConfiguration->hasSession($request)) {
       return [];
     }