core/modules/contact/src/Controller/ContactController.php | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/core/modules/contact/src/Controller/ContactController.php b/core/modules/contact/src/Controller/ContactController.php
index 648a064..8813cd9 100644
--- a/core/modules/contact/src/Controller/ContactController.php
+++ b/core/modules/contact/src/Controller/ContactController.php
@@ -106,6 +106,7 @@ public function contactSitePage(ContactFormInterface $contact_form = NULL) {
 
     $form = $this->entityFormBuilder()->getForm($message);
     $form['#title'] = String::checkPlain($contact_form->label());
+    $form['#cache']['contexts'][] = 'user.roles';
     $form['#cache']['tags'] = Cache::mergeTags(isset($form['#cache']['tags']) ? $form['#cache']['tags'] : [],  $config->getCacheTags());
     return $form;
   }
@@ -141,6 +142,7 @@ public function contactPersonalPage(UserInterface $user) {
 
     $form = $this->entityFormBuilder()->getForm($message);
     $form['#title'] = $this->t('Contact @username', array('@username' => $user->getUsername()));
+    $form['#cache']['contexts'][] = 'user.roles';
     return $form;
   }
 
@@ -150,6 +152,9 @@ public function contactPersonalPage(UserInterface $user) {
    * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
    */
   protected function contactFloodControl() {
+    // Flood control is incompatible with page caching.
+    \Drupal::service('page_cache_kill_switch')->trigger();
+
     $limit = $this->config('contact.settings')->get('flood.limit');
     $interval = $this->config('contact.settings')->get('flood.interval');
     if (!$this->flood->isAllowed('contact', $limit, $interval)) {