diff --git a/core/modules/system/lib/Drupal/system/Plugin/ImageToolkit/GDToolkit.php b/core/modules/system/lib/Drupal/system/Plugin/ImageToolkit/GDToolkit.php
index 322b0bb..6e1a572 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/ImageToolkit/GDToolkit.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/ImageToolkit/GDToolkit.php
@@ -10,7 +10,6 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Image\ImageInterface;
 use Drupal\Component\Plugin\PluginBase;
-use Drupal\Component\Utility\Unicode;
 use Drupal\system\Annotation\ImageToolkit;
 use Drupal\system\Plugin\ImageToolkitInterface;
 
@@ -222,18 +221,14 @@ public function getInfo(ImageInterface $image) {
     $data = getimagesize($image->getSource());
 
     if (isset($data) && is_array($data)) {
-      // image_type_to_extension(IMAGETYPE_JPEG) always returns 'jpeg' even if
-      // the extension is 'jpg'. Extract the extension from the filename.
-      if ($data[2] == IMAGETYPE_JPEG) {
-        $extension = pathinfo($image->getSource(), PATHINFO_EXTENSION);
-        // It may be a temporary file, without extension. Fallback to 'jpg'.
-        $extension = Unicode::strtolower($extension);
-        $extension = in_array($extension, array('jpg', 'jpeg')) ? $extension : 'jpg';
-      }
-      else {
-        $extension = image_type_to_extension($data[2], FALSE);
-        $extension = in_array($extension, static::getAvailableExtensions()) ? $extension : '';
+      $extension = image_type_to_extension($data[2], FALSE);
+      // image_type_to_extension(IMAGETYPE_JPEG) returns 'jpeg' while we want to
+      // return 'jpg' (for reasons of backwards compatibility).
+      if ($extension === 'jpeg') {
+        $extension = 'jpg';
       }
+      // Check if this image format is supported.
+      $extension = in_array($extension, static::getAvailableExtensions()) ? $extension : '';
       $details = array(
         'width'     => $data[0],
         'height'    => $data[1],
diff --git a/core/modules/system/lib/Drupal/system/Plugin/ImageToolkitInterface.php b/core/modules/system/lib/Drupal/system/Plugin/ImageToolkitInterface.php
index a1ddbd0..e582d23 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/ImageToolkitInterface.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/ImageToolkitInterface.php
@@ -182,7 +182,7 @@ function getInfo(ImageInterface $image);
   public static function isAvailable();
 
   /**
-   * Returns a list of image extensions handled by the image toolkit.
+   * Returns a list of lower case image extensions supported by the toolkit.
    *
    * @return array
    *   An array of available image extensions.
diff --git a/core/modules/system/lib/Drupal/system/Tests/Image/ToolkitGdTest.php b/core/modules/system/lib/Drupal/system/Tests/Image/ToolkitGdTest.php
index 648b2f6..589c843 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Image/ToolkitGdTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Image/ToolkitGdTest.php
@@ -264,7 +264,7 @@ function testManipulations() {
         $this->assertTrue($correct_dimensions_object, format_string('Image %file object after %action action is reporting the proper height and width values.', array('%file' => $file, '%action' => $op)));
 
         // JPEG colors will always be messed up due to compression.
-        if (!in_array($image->getExtension(), array('jpg', 'jpeg'))) {
+        if ($image->getExtension() != 'jpg') {
           // Now check each of the corners to ensure color correctness.
           foreach ($values['corners'] as $key => $corner) {
             // Get the location of the corner.
@@ -317,7 +317,7 @@ public function testExtensions() {
 
     foreach ($files as $extension => $file) {
       $image = $image_factory->get($file);
-      $expected = $extension ?: 'jpg';
+      $expected = in_array($extension, array('jpeg', '')) ? 'jpg' : $extension;
       $this->assertEqual($image->getExtension(), $expected);
     }
   }
diff --git a/core/modules/system/tests/modules/image_test/lib/Drupal/image_test/Plugin/ImageToolkit/TestToolkit.php b/core/modules/system/tests/modules/image_test/lib/Drupal/image_test/Plugin/ImageToolkit/TestToolkit.php
index f5b336e..57c4abb 100644
--- a/core/modules/system/tests/modules/image_test/lib/Drupal/image_test/Plugin/ImageToolkit/TestToolkit.php
+++ b/core/modules/system/tests/modules/image_test/lib/Drupal/image_test/Plugin/ImageToolkit/TestToolkit.php
@@ -10,7 +10,6 @@
 use Drupal\Core\Annotation\Translation;
 use Drupal\Core\Image\ImageInterface;
 use Drupal\Component\Plugin\PluginBase;
-use Drupal\Component\Utility\Unicode;
 use Drupal\system\Annotation\ImageToolkit;
 use Drupal\system\Plugin\ImageToolkitInterface;
 
@@ -47,18 +46,14 @@ public function getInfo(ImageInterface $image) {
     $data = getimagesize($image->getSource());
 
     if (isset($data) && is_array($data)) {
-      // image_type_to_extension(IMAGETYPE_JPEG) always returns 'jpeg' even if
-      // the extension is 'jpg'. Extract the extension from the filename.
-      if ($data[2] == IMAGETYPE_JPEG) {
-        $extension = pathinfo($image->getSource(), PATHINFO_EXTENSION);
-        // It may be a temporary file, without extension. Fallback to 'jpg'.
-        $extension = Unicode::strtolower($extension);
-        $extension = in_array($extension, array('jpg', 'jpeg')) ? $extension : 'jpg';
-      }
-      else {
-        $extension = image_type_to_extension($data[2], FALSE);
-        $extension = in_array($extension, self::getAvailableExtensions()) ? $extension : '';
+      $extension = image_type_to_extension($data[2], FALSE);
+      // image_type_to_extension(IMAGETYPE_JPEG) returns 'jpeg' while we want to
+      // return 'jpg' (for reasons of backwards compatibility).
+      if ($extension === 'jpeg') {
+        $extension = 'jpg';
       }
+      // Check if this image format is supported.
+      $extension = in_array($extension, static::getAvailableExtensions()) ? $extension : '';
       $details = array(
         'width'     => $data[0],
         'height'    => $data[1],