core/modules/big_pipe/src/Render/BigPipe.php | 32 +++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/core/modules/big_pipe/src/Render/BigPipe.php b/core/modules/big_pipe/src/Render/BigPipe.php
index 5e3cc12..5b45678 100644
--- a/core/modules/big_pipe/src/Render/BigPipe.php
+++ b/core/modules/big_pipe/src/Render/BigPipe.php
@@ -538,15 +538,41 @@ protected function renderPlaceholder($placeholder, array $placeholder_render_arr
   protected function getPlaceholderOrder($html) {
     $fragments = explode('<div data-big-pipe-placeholder-id="', $html);
     array_shift($fragments);
-    $order = [];
+    $placeholders = [];
 
     foreach ($fragments as $fragment) {
       $t = explode('"></div>', $fragment, 2);
       $placeholder = $t[0];
-      $order[] = $placeholder;
+      $placeholders[] = $placeholder;
     }
+    $placeholders = array_unique($placeholders);
+
+    // The 'status messages' placeholder' needs to be special cased, because it
+    // depends on global state that can be modified when other placeholders are
+    // being rendered: any code can add messages to render.
+    // This violates the principle that each lazy builder must be able to render
+    // itself in isolation, and therefore in any order. However, we cannot
+    // change the way drupal_set_message() works in the Drupal 8 cycle. So we
+    // have to accommodate its special needs.
+    // Allowing placeholders to be rendered in a particular order (in this case:
+    // last) would violate this isolation principle. Thus a monopoly is granted
+    // to this one special case, with this hard-coded solution.
+    // @see \Drupal\Core\Render\Element\StatusMessages
+    // @see \Drupal\Core\Render\Renderer::replacePlaceholders()
+    // @see https://www.drupal.org/node/2712935#comment-11368923
+    $possible_message_placeholders = [
+      'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]&amp;token=a8c34b5e',
+      'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]=status&amp;token=a26f536e',
+      'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]=warning&amp;token=67320bbd',
+      'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&amp;args[0]=error&amp;token=35b549cb',
+    ];
 
-    return array_unique($order);
+    // Render placeholders in the appropriate order.
+    $ordered_placeholders = array_merge(
+      array_diff($placeholders, $possible_message_placeholders),
+      array_intersect($placeholders, $possible_message_placeholders)
+    );
+    return $ordered_placeholders;
   }
 
 }