diff --git a/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php b/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php
index a553bff..b24ecc2 100644
--- a/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php
+++ b/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php
@@ -19,7 +19,7 @@ class PlaceholderStrategyManager implements PlaceholderStrategyInterface {
    *
    * @var \Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface[]
    */
-  protected $placeholderStrategies;
+  protected $placeholderStrategies = [];
 
   /**
    * Adds a placeholder strategy to use.
@@ -39,10 +39,8 @@ public function processPlaceholders(array $placeholders) {
       return [];
     }
 
-    // In case there are no placeholder strategies, return all placeholders.
-    if (empty($this->placeholderStrategies)) {
-      return $placeholders;
-    }
+    // Assert that there is at least one strategy.
+    assert('!empty($this->placeholderStrategies)', 'At least one placeholder strategy needs to be present.');
 
     $new_placeholders = [];
 
@@ -51,6 +49,7 @@ public function processPlaceholders(array $placeholders) {
     // and this uses a variation of the "chain of responsibility" design pattern.
     foreach ($this->placeholderStrategies as $strategy) {
       $processed_placeholders = $strategy->processPlaceholders($placeholders);
+      assert('array_intersect_key($processed_placeholders, $placeholders) === $processed_placeholders', 'Processed placeholders need to be a subset of all placeholders.');
       $placeholders = array_diff_key($placeholders, $processed_placeholders);
       $new_placeholders += $processed_placeholders;
 
diff --git a/core/lib/Drupal/Core/Render/Renderer.php b/core/lib/Drupal/Core/Render/Renderer.php
index 120b204..bb8f1ff 100644
--- a/core/lib/Drupal/Core/Render/Renderer.php
+++ b/core/lib/Drupal/Core/Render/Renderer.php
@@ -164,8 +164,10 @@ public function renderPlain(&$elements) {
    *   The updated $elements.
    *
    * @see ::replacePlaceholders()
+   *
+   * @todo Make public as part of https://www.drupal.org/node/2469431
    */
-  public function renderPlaceholder($placeholder, array $elements) {
+  protected function renderPlaceholder($placeholder, array $elements) {
     // Get the render array for the given placeholder
     $placeholder_elements = $elements['#attached']['placeholders'][$placeholder];
 
@@ -274,6 +276,12 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
       $cached_element = $this->renderCache->get($elements);
       if ($cached_element !== FALSE) {
         $elements = $cached_element;
+        // Only when we're in a root (non-recursive) Renderer::render() call,
+        // placeholders must be processed, to prevent breaking the render cache
+        // in case of nested elements with #cache set.
+        if ($is_root_call) {
+          $this->replacePlaceholders($elements);
+        }
         // Mark the element markup as safe if is it a string.
         if (is_string($elements['#markup'])) {
           $elements['#markup'] = SafeString::create($elements['#markup']);
@@ -284,14 +292,6 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
         // Render cache hit, so rendering is finished, all necessary info
         // collected!
         $context->bubble();
-
-        // Only when we're in a root (non-recursive) Renderer::render() call,
-        // placeholders must be processed, to prevent breaking the render cache
-        // in case of nested elements with #cache set.
-        if ($is_root_call) {
-          $this->replacePlaceholders($elements);
-        }
-
         return $elements['#markup'];
       }
     }
@@ -533,16 +533,6 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
       $this->renderCache->set($elements, $pre_bubbling_elements);
     }
 
-    if ($is_root_call) {
-      // @todo remove as part of https://www.drupal.org/node/2511330.
-      if ($context->count() !== 1) {
-        throw new \LogicException('A stray drupal_render() invocation with $is_root_call = TRUE is causing bubbling of attached assets to break.');
-      }
-    }
-
-    // Rendering is finished, all necessary info collected!
-    $context->bubble();
-
     // Only when we're in a root (non-recursive) Renderer::render() call,
     // placeholders must be processed, to prevent breaking the render cache in
     // case of nested elements with #cache set.
@@ -554,8 +544,15 @@ protected function doRender(&$elements, $is_root_call = FALSE) {
     // that is handled earlier in Renderer::render().
     if ($is_root_call) {
       $this->replacePlaceholders($elements);
+      // @todo remove as part of https://www.drupal.org/node/2511330.
+      if ($context->count() !== 1) {
+        throw new \LogicException('A stray drupal_render() invocation with $is_root_call = TRUE is causing bubbling of attached assets to break.');
+      }
     }
 
+    // Rendering is finished, all necessary info collected!
+    $context->bubble();
+
     $elements['#printed'] = TRUE;
     return $elements['#markup'];
   }
diff --git a/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php b/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php
index 4018a0b..9e2d0f7 100644
--- a/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php
@@ -23,13 +23,13 @@ class PlaceholderStrategyManagerTest extends UnitTestCase {
    * @dataProvider providerProcessPlaceholders
    */
   public function testProcessPlaceholdersSingleFlush($strategies, $placeholders, $result) {
-    $render_strategy_manager = new PlaceholderStrategyManager();
+    $placeholder_strategy_manager = new PlaceholderStrategyManager();
 
     foreach ($strategies as $strategy) {
-      $render_strategy_manager->addPlaceholderStrategy($strategy);
+      $placeholder_strategy_manager->addPlaceholderStrategy($strategy);
     }
 
-    $this->assertEquals($result, $render_strategy_manager->processPlaceholders($placeholders));
+    $this->assertEquals($result, $placeholder_strategy_manager->processPlaceholders($placeholders));
   }
 
   /**
@@ -43,12 +43,6 @@ public function providerProcessPlaceholders() {
     // Empty placeholders.
     $data[] = [[], [], []];
 
-    // Placeholders but no strategies defined.
-    $placeholders = [
-      'ignore-me' => ['#markup' => 'I-am-a-llama-that-will-be-ignored-by-the-placeholder-strategy-manager.'],
-    ];
-    $data[] = [[], $placeholders, $placeholders];
-
     // Placeholder removing strategy.
     $placeholders = [
       'remove-me' => ['#markup' => 'I-am-a-llama-that-will-be-removed-sad-face.'],
@@ -91,6 +85,9 @@ public function providerProcessPlaceholders() {
     $esi_strategy = $prophecy->reveal();
 
     $prophecy = $this->prophesize('\Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface');
+    $prophecy->processPlaceholders($placeholders)->shouldNotBeCalled();
+    $prophecy->processPlaceholders($result)->shouldNotBeCalled();
+    $prophecy->processPlaceholders([])->shouldNotBeCalled();
     $single_flush_strategy = $prophecy->reveal();
 
     $data[] = [[$esi_strategy, $single_flush_strategy], $placeholders, $result];
@@ -126,4 +123,47 @@ public function providerProcessPlaceholders() {
     return $data;
   }
 
+  /**
+   * @covers ::processPlaceholders
+   *
+   * @expectedException \AssertionError
+   * @expectedExceptionMessage At least one placeholder strategy needs to be present.
+   */
+  public function testProcessPlaceholdersNoStrategies() {
+    // Placeholders but no strategies defined.
+    $placeholders = [
+      'assert-me' => ['#markup' => 'I-am-a-llama-that-will-lead-to-an-assertion-by-the-placeholder-strategy-manager.'],
+    ];
+
+    $placeholder_strategy_manager = new PlaceholderStrategyManager();
+    $placeholder_strategy_manager->processPlaceholders($placeholders);
+  }
+
+  /**
+   * @covers ::processPlaceholders
+   *
+   * @expectedException \AssertionError
+   * @expectedExceptionMessage Processed placeholders need to be a subset of all placeholders.
+   */
+  public function testProcessPlaceholdersWithRoguePlaceholderStrategy() {
+    // Placeholders but no strategies defined.
+    $placeholders = [
+      'assert-me' => ['#markup' => 'llama'],
+    ];
+
+    $result = [
+      'assert-me' => ['#markup' => 'llama'],
+      'new-placeholder' => ['#markup' => 'rogue llama'],
+    ];
+
+    $prophecy = $this->prophesize('\Drupal\Core\Render\Placeholder\PlaceholderStrategyInterface');
+    $prophecy->processPlaceholders($placeholders)->willReturn($result);
+    $rogue_strategy = $prophecy->reveal();
+
+    $placeholder_strategy_manager = new PlaceholderStrategyManager();
+    $placeholder_strategy_manager->addPlaceholderStrategy($rogue_strategy);
+    $placeholder_strategy_manager->processPlaceholders($placeholders);
+  }
+
+
 }