diff --git a/core/modules/image/image.module b/core/modules/image/image.module
index aa05d04..bf32f04 100644
--- a/core/modules/image/image.module
+++ b/core/modules/image/image.module
@@ -1197,6 +1197,8 @@ function theme_image_style($variables) {
   $variables['width'] = $dimensions['width'];
   $variables['height'] = $dimensions['height'];
 
+  $variables['attributes']['class'][] = 'image-style-' . drupal_html_class($variables['style_name']);
+
   // Determine the url for the styled image.
   $variables['uri'] = image_style_url($variables['style_name'], $variables['uri']);
   return theme('image', $variables);
diff --git a/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php b/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php
index 3c61596..ec7f650 100644
--- a/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php
+++ b/core/modules/image/lib/Drupal/image/Tests/ImageThemeFunctionTest.php
@@ -53,7 +53,7 @@ class ImageThemeFunctionTest extends WebTestBase {
       ),
     );
     $rendered_element = render($element);
-    $expected_result = '<a href="' . base_path() . $path . '"><img src="' . $url . '" alt="" /></a>';
+    $expected_result = '<a href="' . base_path() . $path . '"><img class="image-style-test" src="' . $url . '" alt="" /></a>';
     $this->assertEqual($expected_result, $rendered_element, 'theme_image_formatter() correctly renders without title, alt, or path options.');
 
     // Link the image to a fragment on the page, and not a full URL.
@@ -64,7 +64,7 @@ class ImageThemeFunctionTest extends WebTestBase {
       'fragment' => $fragment,
     );
     $rendered_element = render($element);
-    $expected_result = '<a href="#' . $fragment . '"><img src="' . $url . '" alt="" /></a>';
+    $expected_result = '<a href="#' . $fragment . '"><img class="image-style-test" src="' . $url . '" alt="" /></a>';
     $this->assertEqual($expected_result, $rendered_element, 'theme_image_formatter() correctly renders a link fragment.');
   }
 
@@ -78,17 +78,17 @@ class ImageThemeFunctionTest extends WebTestBase {
     $original_uri = file_unmanaged_copy($file->uri, 'public://', FILE_EXISTS_RENAME);
 
     // Create a style.
-    image_style_save(array('name' => 'test'));
-    $url = image_style_url('test', $original_uri);
+    image_style_save(array('name' => 'image_test'));
+    $url = image_style_url('image_test', $original_uri);
 
     $path = $this->randomName();
     $element = array(
       '#theme' => 'image_style',
-      '#style_name' => 'test',
+      '#style_name' => 'image_test',
       '#uri' => $original_uri,
     );
     $rendered_element = render($element);
-    $expected_result = '<img src="' . $url . '" alt="" />';
+    $expected_result = '<img class="image-style-image-test" src="' . $url . '" alt="" />';
     $this->assertEqual($expected_result, $rendered_element, 'theme_image_style() renders an image correctly.');
   }