diff --git a/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Rotate.php b/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Rotate.php
index 94d2f30..3105ed4 100644
--- a/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Rotate.php
+++ b/core/modules/system/src/Plugin/ImageToolkit/Operation/gd/Rotate.php
@@ -63,42 +63,42 @@ protected function execute(array $arguments) {
     // PHP 5.5 GD bug: https://bugs.php.net/bug.php?id=65148: To prevent buggy
     // behavior on negative multiples of 90 degrees we convert any negative
     // angle to a positive one between 0 and 360 degrees.
-    $degrees = $arguments['degrees'];
-    $degrees -= floor($degrees / 360) * 360;
+    $arguments['degrees'] -= floor($arguments['degrees'] / 360) * 360;
 
-    // Set background color argument.
-    if ($arguments['background']) {
-      // Convert the background color argument to RGBA array.
+    // Validate or set background color argument.
+    if (!empty($arguments['background'])) {
+      // Validate the background color: Color::hexToRgb does so for us.
       $background = Color::hexToRgb($arguments['background']) + array( 'alpha' => 0 );
     }
     else {
-      // Background color is not specified: use transparent white as
-      // background.
+      // Background color is not specified: use transparent white as background.
       $background = array('red' => 255, 'green' => 255, 'blue' => 255, 'alpha' => 127);
     }
     // Store the color index for the background as that is what GD uses.
-    $background_idx = imagecolorallocatealpha($this->getToolkit()->getResource(), $background['red'], $background['green'], $background['blue'], $background['alpha']);
+    $arguments['background_idx'] = imagecolorallocatealpha($this->getToolkit()->getResource(), $background['red'], $background['green'], $background['blue'], $background['alpha']);
 
-    // GIF does not work with a transparency channel, but can define 1 color in
-    // its palette to act as transparent.
     if ($this->getToolkit()->getType() === IMAGETYPE_GIF) {
+      // GIF does not work with a transparency channel, but can define 1 color
+      // in its palette to act as transparent.
+
       // Get the current transparent color, if any.
       $gif_transparent_id = imagecolortransparent($this->getToolkit()->getResource());
       if ($gif_transparent_id !== -1) {
-        // The gif already has a transparent color set: remember it to set it
-        // on the rotated image as well.
-        $gif_transparent_color = imagecolorsforindex($this->getToolkit()->getResource(), $gif_transparent_id);
+        // The gif already has a transparent color set: remember it to set it on
+        // the rotated image as well.
+        $arguments['gif_transparent_color'] = imagecolorsforindex($this->getToolkit()->getResource(), $gif_transparent_id);
+
         if ($background['alpha'] >= 127) {
           // We want a transparent background: use the color already set to act
           // as transparent, as background.
-          $background_idx = $gif_transparent_id;
+          $arguments['background_idx'] = $gif_transparent_id;
         }
       }
       else {
         // The gif does not currently have a transparent color set.
         if ($background['alpha'] >= 127) {
           // But as the background is transparent, it should get one.
-          $gif_transparent_color = $background;
+          $arguments['gif_transparent_color'] = $background;
         }
       }
     }
@@ -106,16 +106,15 @@ protected function execute(array $arguments) {
     // Stores the original GD resource.
     $original_res = $this->getToolkit()->getResource();
 
-    // Perform rotation via imagerotate().
-    if ($new_res = imagerotate($this->getToolkit()->getResource(), 360 - $degrees, $background_idx)) {
+    if ($new_res = imagerotate($this->getToolkit()->getResource(), 360 - $arguments['degrees'], $arguments['background_idx'])) {
       $this->getToolkit()->setResource($new_res);
       imagedestroy($original_res);
 
       // GIFs need to reassign the transparent color after performing the
       // rotate, but only do so, if the image already had transparency of its
       // own, or the rotate added a transparent background.
-      if (!empty($gif_transparent_color)) {
-        $transparent_idx = imagecolorexactalpha($this->getToolkit()->getResource(), $gif_transparent_color['red'], $gif_transparent_color['green'], $gif_transparent_color['blue'], $gif_transparent_color['alpha']);
+      if (!empty($arguments['gif_transparent_color'])) {
+        $transparent_idx = imagecolorexactalpha($this->getToolkit()->getResource(), $arguments['gif_transparent_color']['red'], $arguments['gif_transparent_color']['green'], $arguments['gif_transparent_color']['blue'], $arguments['gif_transparent_color']['alpha']);
         imagecolortransparent($this->getToolkit()->getResource(), $transparent_idx);
       }