diff --git a/core/tests/Drupal/Tests/Phpunit5FCTrait.php b/core/tests/Drupal/Tests/Phpunit5FCTrait.php
index ad69d3fac9..0c3b0ad238 100644
--- a/core/tests/Drupal/Tests/Phpunit5FCTrait.php
+++ b/core/tests/Drupal/Tests/Phpunit5FCTrait.php
@@ -42,11 +42,12 @@
    * @return \PHPUnit_Framework_MockObject_MockObject
    *
    * @deprecated in Drupal 8.5.0 and will be removed before Drupal 9.0.0.
-   *   Use \Drupal\Tests\Phpunit5FCTrait::createMock.
+   *   Use \Drupal\Tests\Phpunit5FCTrait::createMock() instead.
    *
    * @see https://www.drupal.org/node/2907725
    */
   public function getMock($originalClassName, $methods = array(), array $arguments = array(), $mockClassName = '', $callOriginalConstructor = TRUE, $callOriginalClone = TRUE, $callAutoload = TRUE, $cloneArguments = FALSE, $callOriginalMethods = FALSE, $proxyTarget = NULL) {
+    @trigger_error('\Drupal\Tests\Phpunit5FCTrait::getMock() in Drupal 8.5.0 and will be removed before Drupal 9.0.0. Use \Drupal\Tests\Phpunit5FCTrait::createMock() instead. See https://www.drupal.org/node/2907725.', E_USER_DEPRECATED);
     return $this->createMock($originalClassName, $methods, $arguments, $mockClassName, $callOriginalConstructor, $callOriginalClone, $callAutoload, $cloneArguments, $callOriginalMethods, $proxyTarget);
   }
 
@@ -98,16 +99,12 @@ 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);
-    // Test classes can have an arbitrary amount of subclasses. We can not
-    // simply test for the existence of the PHPUnit 5 method because this trait
-    // is most likely used among the ancestor classes. So we get the parent of
-    // the parent until this method is not defined any more and we know that
-    // the method_exists check is performed on \PHPUnit\Framework\TestCase.
-    while (method_exists($parent, 'isPhpunit5')) {
+    // 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)) {
       $parent = get_parent_class($parent);
     }
-    // Finally we are not checking the method defined in this trait and we can
-    // determine if the running test class is extending from PHPUnit 5 or not.
     return method_exists($parent, 'createMock');
   }
 
diff --git a/core/tests/Drupal/Tests/Phpunit5FCTraitTest.php b/core/tests/Drupal/Tests/Phpunit5FCTraitTest.php
index 7ae5e7e3db..cf02b4e0bb 100644
--- a/core/tests/Drupal/Tests/Phpunit5FCTraitTest.php
+++ b/core/tests/Drupal/Tests/Phpunit5FCTraitTest.php
@@ -16,6 +16,8 @@ class Phpunit5FCTraitTest extends UnitTestCase {
    *
    * @covers ::getMock
    * @dataProvider providerMockVersions
+   * @group legacy
+   * @expectedDeprecation \Drupal\Tests\Phpunit5FCTrait::getMock() in Drupal 8.5.0 and will be removed before Drupal 9.0.0. Use \Drupal\Tests\Phpunit5FCTrait::createMock() instead. See https://www.drupal.org/node/2907725.
    */
   public function testGetMock($className, $expected) {
     $class = new $className();
@@ -41,7 +43,9 @@ public function testCreateMock($className, $expected) {
   public function providerMockVersions() {
     return [
       [UnitTestCasePhpunit4TestClass::class, 'PHPUnit 4'],
+      [UnitTestCasePhpunit4TestClassExtends::class, 'PHPUnit 4'],
       [UnitTestCasePhpunit5TestClass::class, 'PHPUnit 5'],
+      [UnitTestCasePhpunit5TestClassExtends::class, 'PHPUnit 5'],
     ];
   }
 
@@ -54,6 +58,7 @@ class Phpunit4TestClass {
   public function getMock($originalClassName) {
     return 'PHPUnit 4';
   }
+
 }
 
 /**
@@ -63,6 +68,7 @@ class Phpunit5TestClass {
   public function createMock($originalClassName) {
     return 'PHPUnit 5';
   }
+
 }
 
 /**
@@ -70,6 +76,13 @@ public function createMock($originalClassName) {
  */
 class UnitTestCasePhpunit4TestClass extends Phpunit4TestClass {
   use Phpunit5FCTrait;
+
+}
+
+/**
+ * Test class for \Drupal\Tests\UnitTestCase with PHPUnit 4.
+ */
+class UnitTestCasePhpunit4TestClassExtends extends UnitTestCasePhpunit4TestClass {
 }
 
 /**
@@ -77,4 +90,11 @@ class UnitTestCasePhpunit4TestClass extends Phpunit4TestClass {
  */
 class UnitTestCasePhpunit5TestClass extends Phpunit5TestClass {
   use Phpunit5FCTrait;
+
+}
+
+/**
+ * Test class for \Drupal\Tests\UnitTestCase with PHPUnit 5.
+ */
+class UnitTestCasePhpunit5TestClassExtends extends UnitTestCasePhpunit5TestClass {
 }