diff --git a/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php b/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php
index 15f1b96..8021568 100644
--- a/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php
+++ b/core/lib/Drupal/Core/ParamConverter/ParamConverterManager.php
@@ -156,7 +156,8 @@ public function enhance(array $defaults, Request $request) {
     // variables in the route path pattern.
     $route = $defaults[RouteObjectInterface::ROUTE_OBJECT];
     $variables = array_flip($route->compile()->getVariables());
-    // Explicitly copy values to break references.
+    // Because foreach copies the values from the array it iterates even if they
+    // are references, use it to break references.
     $raw_variables = array();
     foreach (array_intersect_key($defaults, $variables) as $key => $value) {
       $raw_variables[$key] = $value;
diff --git a/core/tests/Drupal/Tests/Core/ParamConverter/ParamConverterManagerTest.php b/core/tests/Drupal/Tests/Core/ParamConverter/ParamConverterManagerTest.php
index 942a3f2..71671a0 100644
--- a/core/tests/Drupal/Tests/Core/ParamConverter/ParamConverterManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/ParamConverter/ParamConverterManagerTest.php
@@ -151,6 +151,7 @@ public function providerTestGetConverter() {
    * @see \Drupal\Core\ParamConverter\ParamConverterManager::enhance().
    */
   public function testEnhance() {
+    // Create a mock route using a mock parameter converter.
     $converter = $this->getMock('Drupal\Core\ParamConverter\ParamConverterInterface');
     $this->manager->addConverter('test_convert');
 
@@ -181,8 +182,11 @@ public function testEnhance() {
 
     $defaults = $this->manager->enhance($defaults, $request);
 
+    // The value of 1 should be upcast to the User object for UID 1.
     $this->assertSame($entity, $defaults['id']);
+    // The parameter for the user ID should be stored in the raw variables.
     $this->assertTrue($defaults['_raw_variables']->has('id'));
+    // The raw non-upcasted value for the user should be the UID.
     $this->assertEquals(1, $defaults['_raw_variables']->get('id'));
   }