core/modules/system/src/Tests/Common/PageRenderTest.php | 4 ++--
 core/modules/system/system.module                       | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/core/modules/system/src/Tests/Common/PageRenderTest.php b/core/modules/system/src/Tests/Common/PageRenderTest.php
index cf8d848..09dd9b3 100644
--- a/core/modules/system/src/Tests/Common/PageRenderTest.php
+++ b/core/modules/system/src/Tests/Common/PageRenderTest.php
@@ -73,7 +73,7 @@ function assertPageRenderHookExceptions($module, $hook) {
     }
     catch (\LogicException $e) {
       $this->pass($assertion);
-      $this->assertEqual($e->getMessage(), 'Only #attached and #post_render_cache may be set in ' . $hook . '()');
+      $this->assertEqual($e->getMessage(), 'Only #attached and #post_render_cache may be set in ' . $hook . '().');
     }
     \Drupal::state()->set('bc_test.' . $hook . '.descendant_attached', FALSE);
 
@@ -87,7 +87,7 @@ function assertPageRenderHookExceptions($module, $hook) {
     }
     catch (\LogicException $e) {
       $this->pass($assertion);
-      $this->assertEqual($e->getMessage(), 'Only #attached and #post_render_cache may be set in ' . $hook . '()');
+      $this->assertEqual($e->getMessage(), 'Only #attached and #post_render_cache may be set in ' . $hook . '().');
     }
     \Drupal::state()->set($module . '.' . $hook . '.render_array', FALSE);
   }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 5300b40..0d41bba 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -561,12 +561,12 @@ function system_page_attachments(array &$page) {
     $function($attachments);
   }
   if (array_diff(array_keys($attachments), ['#attached', '#post_render_cache']) !== []) {
-    throw new \LogicException('Only #attached and #post_render_cache may be set in hook_page_build()');
+    throw new \LogicException('Only #attached and #post_render_cache may be set in hook_page_build().');
   }
   \Drupal::moduleHandler()->alter('page', $attachments);
   \Drupal::theme()->alter('page', $attachments);
   if (array_diff(array_keys($attachments), ['#attached', '#post_render_cache']) !== []) {
-    throw new \LogicException('Only #attached and #post_render_cache may be set in hook_page_alter()');
+    throw new \LogicException('Only #attached and #post_render_cache may be set in hook_page_alter().');
   }
   if (isset($attachments['#attached'])) {
     $page['#attached'] = $attachments['#attached'];