diff --git a/core/tests/Drupal/Tests/Phpunit5FCTrait.php b/core/tests/Drupal/Tests/Phpunit5FCTrait.php
index 8eddcbe30c..17f7b73577 100644
--- a/core/tests/Drupal/Tests/Phpunit5FCTrait.php
+++ b/core/tests/Drupal/Tests/Phpunit5FCTrait.php
@@ -98,10 +98,12 @@ public function createMock($originalClassName, $methods = array(), array $argume
   private function isPhpunit5() {
     // Get the parent class of the currently running test class.
     $parent = get_parent_class($this);
-    // Ensure that we do the method exists check of the first parent of $this
-    // that does not use this trait. Most often the check will be made on
-    // \PHPUnit\Framework\TestCase.;
-    while (in_array(__TRAIT__, class_uses($parent), TRUE)) {
+    // Ensure that the method_exists() check on PHPUnit 5's createMock method is
+    // carried out on the first parent of $this that does not have access to
+    // this trait's methods. This is because the trait also has a method called
+    // createMock(). Most often the check will be made on
+    // \PHPUnit\Framework\TestCase.
+    while (method_exists($parent, 'isPhpunit5')) {
       $parent = get_parent_class($parent);
     }
     return method_exists($parent, 'createMock');