diff --git a/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php b/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php
index ed34e60..bcb1a00 100644
--- a/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php
+++ b/core/lib/Drupal/Core/Render/Placeholder/PlaceholderStrategyManager.php
@@ -39,10 +39,16 @@ public function processPlaceholders(array $placeholders) {
       return [];
     }
 
+    // In case there are no placeholder strategies, return all placeholders.
+    if (empty($this->placeholderStrategies)) {
+      return $placeholders;
+    }
+
     $new_placeholders = [];
 
     // Give each render strategy a chance to replace all not-yet replaced
-    // placeholders.
+    // placeholders. The order of placeholder strategies is well defined
+    // and this uses a variation of the "chain of responsibility" design pattern.
     foreach ($this->placeholderStrategies as $strategy) {
       $processed_placeholders = $strategy->processPlaceholders($placeholders);
       $placeholders = array_diff_key($placeholders, $processed_placeholders);
diff --git a/core/lib/Drupal/Core/Render/Placeholder/SingleFlushStrategy.php b/core/lib/Drupal/Core/Render/Placeholder/SingleFlushStrategy.php
index 2c47c8d..61fea0f 100644
--- a/core/lib/Drupal/Core/Render/Placeholder/SingleFlushStrategy.php
+++ b/core/lib/Drupal/Core/Render/Placeholder/SingleFlushStrategy.php
@@ -10,7 +10,8 @@
 /**
  * Defines the 'single_flush' placeholder strategy.
  *
- * This is the last strategy that always replaces all remaining placeholders.
+ * This is designed to be the fallback strategy, so should have the lowest
+ * priority.
  */
 class SingleFlushStrategy implements PlaceholderStrategyInterface {
 
diff --git a/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php b/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php
index a4a5be1..4018a0b 100644
--- a/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/Placeholder/PlaceholderStrategyManagerTest.php
@@ -43,6 +43,12 @@ 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.'],