diff --git a/Models/ThemeConfig/Json/LayerConfigJson.ts b/Models/ThemeConfig/Json/LayerConfigJson.ts
index 36dc8ea3d..e5e177221 100644
--- a/Models/ThemeConfig/Json/LayerConfigJson.ts
+++ b/Models/ThemeConfig/Json/LayerConfigJson.ts
@@ -260,7 +260,7 @@ export interface LayerConfigJson {
                   /**
                    * The type of background picture
                    */
-                  preferredBackground:
+                  preferredBackground?:
                       | "osmbasedmap"
                       | "photo"
                       | "historicphoto"