diff --git a/core/modules/responsive_image/src/Entity/ResponsiveImageStyle.php b/core/modules/responsive_image/src/Entity/ResponsiveImageStyle.php
index f3a2084aa57efe67183babff1bb23f5ce656cfc1..f585bc240a38af148a7eb8a06af880d35c1387d9 100644
--- a/core/modules/responsive_image/src/Entity/ResponsiveImageStyle.php
+++ b/core/modules/responsive_image/src/Entity/ResponsiveImageStyle.php
@@ -112,6 +112,7 @@ public function addImageStyleMapping($breakpoint_id, $multiplier, array $image_s
           'breakpoint_id' => $breakpoint_id,
           'multiplier' => $multiplier,
         ) + $image_style_mapping;
+        $this->keyedImageStyleMappings = NULL;
         return $this;
       }
     }
diff --git a/core/modules/responsive_image/tests/src/Unit/ResponsiveImageStyleConfigEntityUnitTest.php b/core/modules/responsive_image/tests/src/Unit/ResponsiveImageStyleConfigEntityUnitTest.php
index 63580a87203fd19489256ab50b9d0880ccbff041..71e81edcec0eab545459c553889dd9907b4486b6 100644
--- a/core/modules/responsive_image/tests/src/Unit/ResponsiveImageStyleConfigEntityUnitTest.php
+++ b/core/modules/responsive_image/tests/src/Unit/ResponsiveImageStyleConfigEntityUnitTest.php
@@ -252,6 +252,19 @@ public function testGetKeyedImageStyleMappings() {
       'image_mapping' => 'medium',
     );
     $this->assertEquals($expected, $entity->getKeyedImageStyleMappings());
+
+    // Overwrite a mapping to ensure keyed mapping static cache is rebuilt.
+    $entity->addImageStyleMapping('test_breakpoint2', '2x', array(
+      'image_mapping_type' => 'image_style',
+      'image_mapping' => 'large',
+    ));
+    $expected['test_breakpoint2']['2x'] = array(
+      'breakpoint_id' => 'test_breakpoint2',
+      'multiplier' => '2x',
+      'image_mapping_type' => 'image_style',
+      'image_mapping' => 'large',
+    );
+    $this->assertEquals($expected, $entity->getKeyedImageStyleMappings());
   }
 
   /**