diff --git a/core/modules/responsive_image/src/ResponsiveImageStyleForm.php b/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
index d8c3a06..bec62ed 100644
--- a/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
+++ b/core/modules/responsive_image/src/ResponsiveImageStyleForm.php
@@ -128,7 +128,7 @@ public function form(array $form, FormStateInterface $form_state) {
           ),
           '#default_value' => isset($image_style_mapping['image_mapping_type']) ? $image_style_mapping['image_mapping_type'] : '_none',
         );
-        $form['keyed_styles'][$breakpoint_id][$multiplier]['image_mapping'] = array(
+        $form['keyed_styles'][$breakpoint_id][$multiplier]['image_style'] = array(
           '#type' => 'select',
           '#title' => $this->t('Image style'),
           '#options' => $image_styles,
@@ -243,7 +243,11 @@ public function save(array $form, FormStateInterface $form_state) {
             $responsive_image_style->addImageStyleMapping($breakpoint_id, $multiplier, $mapping);
           }
           else if ($image_style_mapping['image_mapping_type'] == 'image_style') {
-            $responsive_image_style->addImageStyleMapping($breakpoint_id, $multiplier, $image_style_mapping);
+            $mapping = array(
+              'image_mapping_type' => 'image_style',
+              'image_mapping' => $image_style_mapping['image_style']
+            );
+            $responsive_image_style->addImageStyleMapping($breakpoint_id, $multiplier, $mapping);
           }
         }
       }
diff --git a/core/modules/responsive_image/src/Tests/ResponsiveImageAdminUITest.php b/core/modules/responsive_image/src/Tests/ResponsiveImageAdminUITest.php
index 82627af..15daedd 100644
--- a/core/modules/responsive_image/src/Tests/ResponsiveImageAdminUITest.php
+++ b/core/modules/responsive_image/src/Tests/ResponsiveImageAdminUITest.php
@@ -81,7 +81,7 @@ public function testResponsiveImageAdmin() {
       // Check if the radio buttons are present.
       $this->assertFieldByName('keyed_styles[responsive_image_test_module.' . $case[0] . '][' . $case[1] . '][image_mapping_type]', '');
       // Check if the image style dropdowns are present.
-      $this->assertFieldByName('keyed_styles[responsive_image_test_module.' . $case[0] . '][' . $case[1] . '][image_mapping]', '');
+      $this->assertFieldByName('keyed_styles[responsive_image_test_module.' . $case[0] . '][' . $case[1] . '][image_style]', '');
       // Check if the sizes textfields are present.
       $this->assertFieldByName('keyed_styles[responsive_image_test_module.' . $case[0] . '][' . $case[1] . '][sizes]', '');
       // Check if the image styles checkboxes are present.
@@ -96,19 +96,19 @@ public function testResponsiveImageAdmin() {
       'breakpoint_group' => 'responsive_image_test_module',
       'fallback_image_style' => 'thumbnail',
       'keyed_styles[responsive_image_test_module.mobile][1x][image_mapping_type]' => 'image_style',
-      'keyed_styles[responsive_image_test_module.mobile][1x][image_mapping]' => 'thumbnail',
+      'keyed_styles[responsive_image_test_module.mobile][1x][image_style]' => 'thumbnail',
       'keyed_styles[responsive_image_test_module.narrow][1x][image_mapping_type]' => 'sizes',
       'keyed_styles[responsive_image_test_module.narrow][1x][sizes]' => '(min-width: 700px) 700px, 100vw',
       'keyed_styles[responsive_image_test_module.narrow][1x][sizes_image_styles][large]' => 'large',
       'keyed_styles[responsive_image_test_module.narrow][1x][sizes_image_styles][medium]' => 'medium',
       'keyed_styles[responsive_image_test_module.wide][1x][image_mapping_type]' => 'image_style',
-      'keyed_styles[responsive_image_test_module.wide][1x][image_mapping]' => 'large',
+      'keyed_styles[responsive_image_test_module.wide][1x][image_style]' => 'large',
     );
     $this->drupalPostForm('admin/config/media/responsive-image-style/style_one', $edit, t('Save'));
     $this->drupalGet('admin/config/media/responsive-image-style/style_one');
 
     // Check the mapping for multipliers 1x and 2x for the mobile breakpoint.
-    $this->assertFieldByName('keyed_styles[responsive_image_test_module.mobile][1x][image_mapping]', 'thumbnail');
+    $this->assertFieldByName('keyed_styles[responsive_image_test_module.mobile][1x][image_style]', 'thumbnail');
     $this->assertFieldByName('keyed_styles[responsive_image_test_module.mobile][1x][image_mapping_type]', 'image_style');
     $this->assertFieldByName('keyed_styles[responsive_image_test_module.mobile][2x][image_mapping_type]', '_none');
 
@@ -121,7 +121,7 @@ public function testResponsiveImageAdmin() {
     $this->assertFieldByName('keyed_styles[responsive_image_test_module.narrow][2x][image_mapping_type]', '_none');
 
     // Check the mapping for multipliers 1x and 2x for the wide breakpoint.
-    $this->assertFieldByName('keyed_styles[responsive_image_test_module.wide][1x][image_mapping]', 'large');
+    $this->assertFieldByName('keyed_styles[responsive_image_test_module.wide][1x][image_style]', 'large');
     $this->assertFieldByName('keyed_styles[responsive_image_test_module.wide][1x][image_mapping_type]', 'image_style');
     $this->assertFieldByName('keyed_styles[responsive_image_test_module.wide][2x][image_mapping_type]', '_none');