diff --git a/core/modules/block/block.install b/core/modules/block/block.install
index 38e9a93..29947f0 100644
--- a/core/modules/block/block.install
+++ b/core/modules/block/block.install
@@ -27,6 +27,9 @@ function block_update_8001() {
     if ($visibility = $block->get('visibility')) {
       foreach ($visibility as &$condition) {
         foreach ($condition['context_mapping'] as $key => $context) {
+          if (!isset($context_service_id_map[$key])) {
+            throw new \UnexpectedValueException(sprintf('Encountered an unexpected context mapping key %s', $key));
+          }
           $new_context_id = explode('.', $context, 2);
           $condition['context_mapping'][$key] = '@' . $context_service_id_map[$key] . ':' . $new_context_id[1];
         }
diff --git a/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php b/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php
index b7b655f..34a810b 100644
--- a/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php
+++ b/core/modules/system/tests/fixtures/update/drupal-8.block-context-manager-2354889.php
@@ -11,7 +11,7 @@
 $connection = Database::getConnection();
 
 // Structure of a custom block with visibility settings.
-$block_config = [
+$block_configs = [[
   'uuid' => '9d204071-a923-4707-8200-c298a540fb0c',
   'langcode' => 'en',
   'status' => TRUE,
@@ -70,17 +70,48 @@
       ],
     ],
   ],
-];
+],[
+  'uuid' => 'C499B41D-035E-432E-9462-36410C43C49F',
+  'langcode' => 'en',
+  'status' => TRUE,
+  'dependencies' => [
+    'module' => [
+      'search',
+    ],
+    'theme' => [
+      'bartik',
+    ],
+  ],
+  'id' => 'secondtestfor2354889',
+  'theme' => 'bartik',
+  'region' => 'sidebar_first',
+  'weight' => -6,
+  'provider' => NULL,
+  'plugin' => 'search_form_block',
+  'settings' => [
+    'id' => 'search_form_block',
+    'label' => 'Search',
+    'provider' => 'search',
+    'label_display' => 'visible',
+    'cache' => [
+      'max_age' => -1,
+    ],
+    'status' => TRUE,
+  ],
+  'visibility' => [],
+]];
 
-$connection->insert('config')
-  ->fields(array(
-    'collection',
-    'name',
-    'data',
-  ))
-  ->values(array(
-    'collection' => '',
-    'name' => 'block.block.testfor2354889',
-    'data' => serialize($block_config),
-  ))
-  ->execute();
+foreach ($block_configs as $block_config) {
+  $connection->insert('config')
+    ->fields(array(
+      'collection',
+      'name',
+      'data',
+    ))
+    ->values(array(
+      'collection' => '',
+      'name' => 'block.block.' . $block_config['id'],
+      'data' => serialize($block_config),
+    ))
+    ->execute();
+}