diff --git a/core/modules/image/image.admin.inc b/core/modules/image/image.admin.inc
index ecb72d8..896f4b5 100644
--- a/core/modules/image/image.admin.inc
+++ b/core/modules/image/image.admin.inc
@@ -376,6 +376,12 @@ function image_effect_form_submit($form, &$form_state) {
     'data' => $form_state['values']['data'],
     'weight' => $form_state['values']['weight'],
   );
+
+  // Are we editing an exiting style.
+  if (!empty($form_state['image_effect']['ieid'])) {
+    $effect['ieid'] = $form_state['image_effect']['ieid'];
+  }
+
   image_effect_save($form_state['image_style']['name'], $effect);
   drupal_set_message(t('The image effect was successfully applied.'));
   $form_state['redirect'] = 'admin/config/media/image-styles/edit/' . $form_state['image_style']['name'];
diff --git a/core/modules/image/image.test b/core/modules/image/image.test
index 2c422a7..5f07bec 100644
--- a/core/modules/image/image.test
+++ b/core/modules/image/image.test
@@ -565,6 +565,23 @@ class ImageAdminStylesUnitTest extends ImageFieldTestCase {
     $this->drupalGet('node/' . $nid);
     $this->assertRaw(image_style_url('thumbnail', $node->{$field_name}[LANGUAGE_NOT_SPECIFIED][0]['uri']), t('Image displayed using style replacement style.'));
   }
+
+  /**
+   * Verify that editing an image effect does not cause it to duplicate.
+   */
+  function testEditEffect() {
+    $this->drupalGet('admin/config/media/image-styles/add');
+    $this->drupalPost(NULL, array('name' => 'test_style_effect_edit'), t('Create new style'));
+    $this->drupalPost(NULL, array('new' => 'image_scale_and_crop'), t('Add'));
+    $this->drupalPost(NULL, array('data[width]' => '300', 'data[height]' => '200'), t('Add effect'));
+    $this->assertText(t('Scale and crop 300x200'));
+    // There should normally be only the one edit link on this page initially.
+    $this->clickLink(t('edit'));
+    $this->drupalPost(NULL, array('data[width]' => '360', 'data[height]' => '240'), t('Update effect'));
+    $this->assertText(t('Scale and crop 360x240'));
+    // Check the previous effect is not also retained on this style after editing.
+    $this->assertNoText(t('Scale and crop 300x200'));
+  }
 }
 
 /**