diff --git a/core/lib/Drupal/Core/Image/ImageInterface.php b/core/lib/Drupal/Core/Image/ImageInterface.php
index b8ca6a8..e0b6bda 100644
--- a/core/lib/Drupal/Core/Image/ImageInterface.php
+++ b/core/lib/Drupal/Core/Image/ImageInterface.php
@@ -149,13 +149,16 @@ public function scale($width, $height = NULL, $upscale = FALSE);
   public function scaleAndCrop($width, $height);
 
   /**
-   * Converts an image to a specified format.
+   * Instructs the toolkit to save the image in the specified format.
    *
    * @param string $format
    *   The format to convert to (e.g. 'jpeg', 'png'). Allowed values depend on
    *   the implementation of the convert operation of the image toolkit. For a
    *   working example, see
    *   \Drupal\system\Plugin\ImageToolkit\Operation\gd\Convert.
+   *
+   * @return bool
+   *   TRUE on success, FALSE on failure.
    */
   public function convert($format);
 
diff --git a/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Convert.php b/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Convert.php
index 38dfff8..8ca9754 100644
--- a/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Convert.php
+++ b/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Convert.php
@@ -17,7 +17,7 @@
  *   toolkit = "gd",
  *   operation = "convert",
  *   label = @Translation("Convert"),
- *   description = @Translation("Converts an image to the given format.")
+ *   description = @Translation("Instructs the toolkit to save the image in the specified format.")
  * )
  */
 class Convert extends GDImageToolkitOperationBase {
@@ -47,22 +47,8 @@ protected function validateArguments(array $arguments) {
    * {@inheritdoc}
    */
   protected function execute(array $arguments = array()) {
-    $type = FALSE;
-    switch ($arguments['format']) {
-      case 'jpeg':
-      case 'jpg':
-      case 'jpe':
-        $type = IMAGETYPE_JPEG;
-        break;
-
-      default:
-        $constant = 'IMAGETYPE_' . \Drupal\Component\Utility\Unicode::strtoupper($arguments['format']);
-        if (defined($constant)) {
-          $type = constant($constant);
-        }
-        break;
-    }
-
+    // Make sure we have an image type.
+    $type = $this->getToolkit()->getType();
     if (!$type) {
       return FALSE;
     }
@@ -74,9 +60,8 @@ protected function execute(array $arguments = array()) {
 
     imagedestroy($this->getToolkit()->getResource());
 
-    $this->getToolkit()->setType($type);
     // Update image object.
-    $this->getToolkit()->setResource($res);
+    $this->getToolkit()->setType($type);
 
     return TRUE;
   }