diff --git a/src/core/index.js b/src/core/index.js
index 6e737768..727b56ad 100644
--- a/src/core/index.js
+++ b/src/core/index.js
@@ -25,8 +25,8 @@ module.exports = function SwaggerUI(opts) {
     url: "",
     layout: "BaseLayout",
     validatorUrl: "https://online.swagger.io/validator",
-    configs: {
-    },
+    configs: {},
+    custom: {},
 
     // Initial set of plugins ( TODO rename this, or refactor - we don't need presets _and_ plugins. Its just there for performance.
     // Instead, we can compile the first plugin ( it can be a collection of plugins ), then batch the rest.