diff --git a/core/lib/Drupal/Core/Image/ImageInterface.php b/core/lib/Drupal/Core/Image/ImageInterface.php
index ddcd452..d0e0286 100644
--- a/core/lib/Drupal/Core/Image/ImageInterface.php
+++ b/core/lib/Drupal/Core/Image/ImageInterface.php
@@ -130,7 +130,7 @@ public function save($destination = NULL);
    * @return bool
    *   TRUE on success, FALSE on failure.
    */
-  public function createNew($width, $height, $mime_type = 'png', $transparent_color = '#ffffff');
+  public function createNew($width, $height, $extension = 'png', $transparent_color = '#ffffff');
 
   /**
    * Scales an image while maintaining aspect ratio.
diff --git a/core/modules/system/src/Tests/Image/ToolkitGdTest.php b/core/modules/system/src/Tests/Image/ToolkitGdTest.php
index 898e56b..0d87bb4 100644
--- a/core/modules/system/src/Tests/Image/ToolkitGdTest.php
+++ b/core/modules/system/src/Tests/Image/ToolkitGdTest.php
@@ -299,7 +299,7 @@ function testManipulations() {
           foreach ($values['corners'] as $key => $corner) {
             // The test gif that does not have transparency has yellow where the
             // others have transparent.
-            if ($file === 'image-test-no-transparency.gif' && $corner === $this->transparent && $op !== 'create_new') {
+            if ($file === 'image-test-no-transparency.gif' && $corner === $this->transparent) {
               $corner = $this->yellow;
             }
             // Get the location of the corner.
@@ -330,7 +330,6 @@ function testManipulations() {
         // Check that saved image reloads without raising PHP errors.
         $image_reloaded = $this->imageFactory->get($file_path);
         $resource = $image_reloaded->getToolkit()->getResource();
-
       }
     }
 
@@ -372,7 +371,6 @@ function testManipulations() {
     $this->assertFalse($image->isValid(), 'CreateNew with invalid color hex string fails.');
     $image->createNew(50, 20, 'gif', '#ff0000');
     $this->assertTrue($image->isValid(), 'CreateNew with valid arguments validates the Image.');
-
   }
 
   /**