diff --git a/core/modules/block/block.install b/core/modules/block/block.install
index 40184f9..ceb62ad 100644
--- a/core/modules/block/block.install
+++ b/core/modules/block/block.install
@@ -48,6 +48,8 @@ function block_update_8001() {
   // before/after the update.
   // For updating the status flag of the block in the next update function,
   // however, we can use Entity API.
+  // Contributed modules should leverage hook_update_dependencies() in order to
+  // be executed before block_update_8002().
   $config_factory = \Drupal::configFactory();
   $message = NULL;
   $disabled_blocks = $problematic_visibility_plugins = $backup_values = [];
@@ -116,7 +118,7 @@ function block_update_8002() {
 
   if (count($blocks) > 0) {
     $message = \Drupal::translation()
-      ->translate('Encountered a context mapping key coming probably from a contributed or custom module: One or more mappings could not be updated. Please manually review your visibility settings for the following blocks, which are disabled now:');
+      ->translate('Encountered an unknown context mapping key coming probably from a contributed or custom module: One or more mappings could not be updated. Please manually review your visibility settings for the following blocks, which are disabled now:');
     $message .= '<ul>';
     foreach ($blocks as $disabled_block_id => $disabled_block) {
       $message .= '<li>' . Drupal::translation()
diff --git a/core/modules/block/src/Tests/Update/BlockContextMappingUpdateTest.php b/core/modules/block/src/Tests/Update/BlockContextMappingUpdateTest.php
index 9bad422..495ce67 100644
--- a/core/modules/block/src/Tests/Update/BlockContextMappingUpdateTest.php
+++ b/core/modules/block/src/Tests/Update/BlockContextMappingUpdateTest.php
@@ -36,7 +36,7 @@ protected function setUp() {
    */
   public function testUpdateHookN() {
     $this->runUpdates();
-    $this->assertRaw('Encountered a context mapping key coming probably from a contributed or custom module: One or more mappings could not be updated. Please manually review your visibility settings for the following blocks, which are disabled now:<ul><li>User login (Visibility: baloney.spam)</li></ul>');
+    $this->assertRaw('Encountered an unknown context mapping key coming probably from a contributed or custom module: One or more mappings could not be updated. Please manually review your visibility settings for the following blocks, which are disabled now:<ul><li>User login (Visibility: baloney.spam)</li></ul>');
 
     // Disable maintenance mode.
     \Drupal::state()->set('system.maintenance_mode', FALSE);