diff --git a/core/modules/responsive_image/src/Entity/ResponsiveImageMapping.php b/core/modules/responsive_image/src/Entity/ResponsiveImageMapping.php
index bf15443..0e9dc14 100644
--- a/core/modules/responsive_image/src/Entity/ResponsiveImageMapping.php
+++ b/core/modules/responsive_image/src/Entity/ResponsiveImageMapping.php
@@ -105,14 +105,14 @@ public function addMappingDefinition($breakpoint_id, $multiplier, array $mapping
         $mapping = array(
           'breakpoint_id' => $breakpoint_id,
           'multiplier' => $multiplier,
-        ) + $mapping_definition + $defaults;
+        ) + $mapping_definition;
         return $this;
       }
     }
     $this->mapping_definitions[] = array(
       'breakpoint_id' => $breakpoint_id,
       'multiplier' => $multiplier,
-    ) + $mapping_definition + $defaults;
+    ) + $mapping_definition;
     $this->keyedMappingDefinitions = NULL;
     return $this;
   }