diff --git a/packages/react-json-tree/src/index.tsx b/packages/react-json-tree/src/index.tsx
index 97d562ac..9f3f764a 100644
--- a/packages/react-json-tree/src/index.tsx
+++ b/packages/react-json-tree/src/index.tsx
@@ -7,6 +7,7 @@ import React from 'react';
 import PropTypes from 'prop-types';
 import JSONNode from './JSONNode';
 import createStylingFromTheme from './createStylingFromTheme';
+import './react-base16-styling';
 import {
   Base16Theme,
   invertTheme,
@@ -108,7 +109,7 @@ function getStateFromProps(props: Props) {
       } else {
         theme = {
           ...theme,
-          extend: invertTheme(theme.extend)
+          extend: invertTheme(theme.extend as Base16Theme)
         } as StylingConfig;
       }
     } else if (theme) {
diff --git a/packages/react-json-tree/src/react-base16-styling.d.ts b/packages/react-json-tree/src/react-base16-styling.ts
similarity index 96%
rename from packages/react-json-tree/src/react-base16-styling.d.ts
rename to packages/react-json-tree/src/react-base16-styling.ts
index 86d76a2c..009f5b1f 100644
--- a/packages/react-json-tree/src/react-base16-styling.d.ts
+++ b/packages/react-json-tree/src/react-base16-styling.ts
@@ -33,7 +33,7 @@ declare module 'react-base16-styling' {
     | ((styling: Styling, ...rest: any[]) => Styling);
 
   export type StylingConfig = { [name: string]: StylingValue } & {
-    extend?: string | Base16Theme;
+    extend?: string | Base16Theme | StylingValue;
   };
 
   export type Theme = string | Base16Theme | StylingConfig;