core/modules/image/src/Tests/ImageDimensionsTest.php              | 3 +--
 .../src/Plugin/ImageEffect/NullTestImageEffect.php                | 8 ++++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/core/modules/image/src/Tests/ImageDimensionsTest.php b/core/modules/image/src/Tests/ImageDimensionsTest.php
index 4d6c76b..2db7e24 100644
--- a/core/modules/image/src/Tests/ImageDimensionsTest.php
+++ b/core/modules/image/src/Tests/ImageDimensionsTest.php
@@ -221,8 +221,7 @@ function testImageDimensions() {
     $effect_plugin = $style->getEffect($effect_id);
     $style->deleteImageEffect($effect_plugin);
 
-    // Ensure that an effect with no dimensions callback unsets the dimensions.
-    // This ensures compatibility with 7.0 contrib modules.
+    // Ensure that an effect can unset dimensions.
     $effect = array(
       'id' => 'image_module_test_null',
       'data' => array(),
diff --git a/core/modules/image/tests/modules/image_module_test/src/Plugin/ImageEffect/NullTestImageEffect.php b/core/modules/image/tests/modules/image_module_test/src/Plugin/ImageEffect/NullTestImageEffect.php
index 8fd8632..bcf63ef 100644
--- a/core/modules/image/tests/modules/image_module_test/src/Plugin/ImageEffect/NullTestImageEffect.php
+++ b/core/modules/image/tests/modules/image_module_test/src/Plugin/ImageEffect/NullTestImageEffect.php
@@ -23,6 +23,14 @@ class NullTestImageEffect extends ImageEffectBase {
   /**
    * {@inheritdoc}
    */
+  public function transformDimensions(array &$dimensions) {
+    // Unset image dimensions.
+    $dimensions['width'] = $dimensions['height'] = NULL;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function applyEffect(ImageInterface $image) {
     return TRUE;
   }