diff --git a/core/modules/page_cache/src/StackMiddleware/PageCache.php b/core/modules/page_cache/src/StackMiddleware/PageCache.php
index 120b01e..1c4d8f5 100644
--- a/core/modules/page_cache/src/StackMiddleware/PageCache.php
+++ b/core/modules/page_cache/src/StackMiddleware/PageCache.php
@@ -283,13 +283,15 @@ protected function storeResponse(Request $request, Response $response) {
         $expire = $request_time + $cache_ttl_4xx;
       }
     }
-    else {
-      // The getExpires method could return NULL if Expires header is not set, so
-      // the returned value needs to be checked before calling getTimestamp.
-      $expires = $response->getExpires();
-      $date = ($expires == NULL) ? 0 : $expires->getTimestamp();
+    // The getExpires method could return NULL if Expires header is not set, so
+    // the returned value needs to be checked before calling getTimestamp.
+    elseif ($expires = $response->getExpires()) {
+      $date = $expires->getTimestamp();
       $expire = ($date > $request_time) ? $date : Cache::PERMANENT;
     }
+    else {
+      $expire = Cache::PERMANENT;
+    }
 
     if ($expire === Cache::PERMANENT || $expire > $request_time) {
       $tags = $response->getCacheableMetadata()->getCacheTags();