diff --git a/core/tests/Drupal/Tests/Core/Render/RendererBubblingTest.php b/core/tests/Drupal/Tests/Core/Render/RendererBubblingTest.php
index d659849..1e137d4 100644
--- a/core/tests/Drupal/Tests/Core/Render/RendererBubblingTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/RendererBubblingTest.php
@@ -179,6 +179,7 @@ public function providerTestContextBubblingEdgeCases() {
           'max-age' => Cache::PERMANENT,
         ],
         '#markup' => 'parent',
+        '#safe_cache_properties' => ['#markup'],
       ],
     ];
     $data[] = [$test_element, [], $expected_cache_items];
@@ -202,6 +203,7 @@ public function providerTestContextBubblingEdgeCases() {
           'max-age' => Cache::PERMANENT,
         ],
         '#markup' => '',
+        '#safe_cache_properties' => ['#markup'],
       ],
     ];
     $context_orders = [
@@ -243,6 +245,7 @@ public function providerTestContextBubblingEdgeCases() {
           'max-age' => 3600,
         ],
         '#markup' => 'parent',
+        '#safe_cache_properties' => ['#markup'],
       ],
     ];
     $data[] = [$test_element, ['bar', 'baz', 'foo'], $expected_cache_items];
@@ -291,6 +294,7 @@ public function providerTestContextBubblingEdgeCases() {
           'max-age' => Cache::PERMANENT,
         ],
         '#markup' => 'parent',
+        '#safe_cache_properties' => ['#markup'],
       ],
     ];
     $data[] = [$test_element, ['bar', 'foo'], $expected_cache_items];
@@ -370,6 +374,7 @@ public function testConditionalCacheContextBubblingSelfHealing() {
         'max-age' => Cache::PERMANENT,
       ],
       '#markup' => 'parent',
+      '#safe_cache_properties' => ['#markup'],
     ]);
 
     // Request 2: role B, the grandchild is accessible => bubbled cache
@@ -395,6 +400,7 @@ public function testConditionalCacheContextBubblingSelfHealing() {
         'max-age' => 1800,
       ],
       '#markup' => 'parent',
+      '#safe_cache_properties' => ['#markup'],
     ]);
 
     // Request 3: role A again, the grandchild is inaccessible again => bubbled
@@ -431,6 +437,7 @@ public function testConditionalCacheContextBubblingSelfHealing() {
         'max-age' => Cache::PERMANENT,
       ],
       '#markup' => 'parent',
+      '#safe_cache_properties' => ['#markup'],
     ]);
 
     // Request 4: role C, both the grandchild and the grandgrandchild are
@@ -458,6 +465,7 @@ public function testConditionalCacheContextBubblingSelfHealing() {
         'max-age' => 300,
       ],
       '#markup' => 'parent',
+      '#safe_cache_properties' => ['#markup'],
     ]);
 
     // Request 5: role A again, verifying the merging like we did for request 3.
@@ -477,6 +485,7 @@ public function testConditionalCacheContextBubblingSelfHealing() {
         'max-age' => Cache::PERMANENT,
       ],
       '#markup' => 'parent',
+      '#safe_cache_properties' => ['#markup'],
     ]);
 
     // Request 6: role B again, verifying the merging like we did for request 3.
@@ -496,6 +505,7 @@ public function testConditionalCacheContextBubblingSelfHealing() {
         'max-age' => 1800,
       ],
       '#markup' => 'parent',
+      '#safe_cache_properties' => ['#markup'],
     ]);
   }
 
@@ -529,7 +539,7 @@ public function testBubblingWithPrerender($test_element) {
     // - … is not cached DOES get called.
     \Drupal::state()->set('bubbling_nested_pre_render_cached', FALSE);
     \Drupal::state()->set('bubbling_nested_pre_render_uncached', FALSE);
-    $this->memoryCache->set('cached_nested', ['#markup' => 'Cached nested!', '#attached' => [], '#cache' => ['contexts' => [], 'tags' => []]]);
+    $this->memoryCache->set('cached_nested', ['#markup' => 'Cached nested!', '#attached' => [], '#cache' => ['contexts' => [], 'tags' => []], '#safe_cache_properties' => ['#markup']]);
 
     // Simulate the rendering of an entire response (i.e. a root call).
     $output = $this->renderer->renderRoot($test_element);
diff --git a/core/tests/Drupal/Tests/Core/Render/RendererPlaceholdersTest.php b/core/tests/Drupal/Tests/Core/Render/RendererPlaceholdersTest.php
index a3fe908..2af598c 100644
--- a/core/tests/Drupal/Tests/Core/Render/RendererPlaceholdersTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/RendererPlaceholdersTest.php
@@ -137,6 +137,7 @@ public function providerPlaceholders() {
           'tags' => [],
           'max-age' => Cache::PERMANENT,
         ],
+        '#safe_cache_properties' => ['#markup'],
       ],
     ];
 
@@ -179,6 +180,7 @@ public function providerPlaceholders() {
           'tags' => [],
           'max-age' => Cache::PERMANENT,
         ],
+        '#safe_cache_properties' => ['#markup'],
       ],
     ];
 
@@ -312,6 +314,7 @@ public function testCacheableParent($test_element, $args, $placeholder_cid_keys,
         'tags' => [],
         'max-age' => Cache::PERMANENT,
       ],
+      '#safe_cache_properties' => ['#markup'],
     ];
     $expected_element['#attached']['placeholders'][$expected_placeholder_markup] = $expected_placeholder_render_array;
     $this->assertEquals($cached_element, $expected_element, 'The correct data is cached: the stored #markup and #attached properties are not affected by placeholder #lazy_builder callbacks.');
@@ -579,6 +582,7 @@ public function testRenderChildrenPlaceholdersDifferentArguments() {
         'tags' => [],
         'max-age' => Cache::PERMANENT,
       ],
+      '#safe_cache_properties' => ['#markup'],
     ];
 
     $dom = Html::load($cached_element['#markup']);