diff --git a/types/swagger-ui-express/index.d.ts b/types/swagger-ui-express/index.d.ts
index 8fa2e7ab5b..97a0b66cd9 100644
--- a/types/swagger-ui-express/index.d.ts
+++ b/types/swagger-ui-express/index.d.ts
@@ -1,87 +1,108 @@
-// Type definitions for swagger-ui-express 3.0
+// Type definitions for swagger-ui-express 4.1
 // Project: https://github.com/scottie1984/swagger-ui-express
 // Definitions by: Dmitry Rogozhny <https://github.com/dmitryrogozhny>
+//                 Florian Keller <https://github.com/ffflorian>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.8
 
-import { RequestHandler } from "express";
-import { ServeStaticOptions } from "serve-static";
+import { RequestHandler } from 'express';
+import { ServeStaticOptions } from 'serve-static';
 
-interface JsonObject { [key: string]: any; }
-interface SwaggerUiOptions { [key: string]: any; }
-interface SwaggerOptions { [key: string]: any; }
-
-interface SwaggerUiExpress {
-    /**
-     * Creates a middleware function that returns the pre-generated html file for the Swagger UI page.
-     *
-     * @param swaggerDoc json object with the API schema.
-     * @param opts swagger-ui-express options.
-     * @param options custom swagger options.
-     * @param customCss string with a custom css to embed into the page.
-     * @param customfavIcon link to a custom favicon.
-     * @param swaggerUrl Url of the swagger API schema, can be specified instead of the swaggerDoc.
-     * @param customeSiteTitle custom title for a page
-     * @returns an express middleware function that returns the generated html page.
-     */
-    setup(swaggerDoc?: JsonObject | null,
-        opts?: SwaggerUiOptions | false | null,
-        options?: SwaggerOptions,
-        customCss?: string | false | null,
-        customfavIcon?: string | false | null,
-        swaggerUrl?: string | false | null,
-        customeSiteTitle?: string | false | null): RequestHandler;
-
-    /**
-     * Returns handlers for serving Swagger UI files.
-     * This includes custom initialization js file and static files of Swagger UI.
-     *
-     * @returns Express handlers that process requests and return files for Swagger UI.
-     */
-    serve: RequestHandler[];
-
-    /**
-     * Returns handlers for serving Swagger UI files.
-     * This includes custom initialization js file and static files of Swagger UI.
-     * Additional options are passed to the express.static middleware.
-     *
-     * @param options options object that is passed to the express.static middleware.
-     * @returns Express handlers that process requests and return files for Swagger UI.
-     */
-    serveWithOptions(options: ServeStaticOptions): RequestHandler[];
-
-    /**
-     * Generates the custom html page for the UI API.
-     *
-     * @param swaggerDoc json object with the API schema.
-     * @param opts swagger-ui-express options.
-     * @param options custom swagger options.
-     * @param customCss string with a custom css to embed into the page.
-     * @param customfavIcon link to a custom favicon.
-     * @param swaggerUrl Url of the swagger API schema, can be specified instead of the swaggerDoc.
-     * @param customeSiteTitle custom title for a page
-     * @returns the generated html page.
-     */
-    generateHTML(swaggerDoc?: JsonObject | null,
-        opts?: SwaggerUiOptions | false | null,
-        options?: SwaggerOptions,
-        customCss?: string | false | null,
-        customfavIcon?: string | false | null,
-        swaggerUrl?: string | false | null,
-        customeSiteTitle?: string | false | null): string;
-
-    /**
-     * Returns handlers for serving Swagger UI files.
-     * This includes custom initialization js file and static files of Swagger UI.
-     * Additional options object is passed to Swagger UI.
-     *
-     * @param swaggerDoc json object with the Swagger API schema.
-     * @param opts options to pass to Swagger UI.
-     * @returns Express handlers that process requests and return files for Swagger UI.
-     */
-    serveFiles(swaggerDoc?: JsonObject, opts?: SwaggerUiOptions): RequestHandler[];
+export interface JsonObject {
+    [key: string]: any;
 }
 
-declare const swaggerUiExpress: SwaggerUiExpress;
+export interface SwaggerOptions {
+    [key: string]: any;
+}
 
-export = swaggerUiExpress;
+export interface SwaggerUiOptions {
+    customCss?: string;
+    customCssUrl?: string;
+    customfavIcon?: string;
+    customJs?: string;
+    customSiteTitle?: string;
+    isExplorer?: boolean;
+    options?: SwaggerOptions;
+    swaggerUrl?: string;
+    swaggerUrls?: string[];
+}
+
+/**
+ * Creates a middleware function that returns the pre-generated HTML file for the Swagger UI page.
+ *
+ * @param swaggerDoc JSON object with the API schema.
+ * @param opts swagger-ui-express options.
+ * @param options custom Swagger options.
+ * @param customCss string with a custom CSS to embed into the page.
+ * @param customfavIcon link to a custom favicon.
+ * @param swaggerUrl URL of the Swagger API schema, can be specified instead of the swaggerDoc.
+ * @param customSiteTitle custom title for a page.
+ * @returns an express middleware function that returns the generated HTML page.
+ */
+export function setup(
+    swaggerDoc?: JsonObject,
+    opts?: SwaggerUiOptions,
+    options?: SwaggerOptions,
+    customCss?: string,
+    customfavIcon?: string,
+    swaggerUrl?: string,
+    customSiteTitle?: string,
+): RequestHandler;
+
+/** @deprecated */
+export function setup(swaggerDoc?: JsonObject, isExplorer?: boolean): RequestHandler;
+
+/**
+ * Returns handlers for serving Swagger UI files.
+ * This includes the custom initialization JS file and static files of Swagger UI.
+ *
+ * @returns Express handlers that process requests and return files for Swagger UI.
+ */
+export const serve: RequestHandler[];
+
+/**
+ * Returns handlers for serving Swagger UI files.
+ * This includes custom initialization js file and static files of Swagger UI.
+ * Additional options are passed to the `express.static` middleware.
+ *
+ * @param options options object that is passed to the `express.static` middleware.
+ * @returns Express handlers that process requests and return files for Swagger UI.
+ */
+export function serveWithOptions(options: ServeStaticOptions): RequestHandler[];
+
+/**
+ * Generates the custom HTML page for the UI API.
+ *
+ * @param swaggerDoc JSON object with the API schema.
+ * @param opts swagger-ui-express options.
+ * @param options custom Swagger options.
+ * @param customCss string with a custom CSS to embed into the page.
+ * @param customfavIcon link to a custom favicon.
+ * @param swaggerUrl URL of the Swagger API schema, can be specified instead of the swaggerDoc.
+ * @param customSiteTitle custom title for a page.
+ * @returns the generated HTML page.
+ */
+export function generateHTML(
+    swaggerDoc?: JsonObject,
+    opts?: SwaggerUiOptions,
+    options?: SwaggerOptions,
+    customCss?: string,
+    customfavIcon?: string,
+    swaggerUrl?: string,
+    customSiteTitle?: string,
+): string;
+
+/** @deprecated */
+export function generateHTML(swaggerDoc?: JsonObject, isExplorer?: boolean): RequestHandler;
+
+/**
+ * Returns handlers for serving Swagger UI files.
+ * This includes custom initialization js file and static files of Swagger UI.
+ * Additional options object is passed to Swagger UI.
+ *
+ * @param swaggerDoc JSON object with the Swagger API schema.
+ * @param opts options to pass to Swagger UI.
+ * @returns Express handlers that process requests and return files for Swagger UI.
+ */
+export function serveFiles(swaggerDoc?: JsonObject, opts?: SwaggerUiOptions): RequestHandler[];
diff --git a/types/swagger-ui-express/swagger-ui-express-tests.ts b/types/swagger-ui-express/swagger-ui-express-tests.ts
index f91128205c..e1ca950119 100644
--- a/types/swagger-ui-express/swagger-ui-express-tests.ts
+++ b/types/swagger-ui-express/swagger-ui-express-tests.ts
@@ -7,60 +7,82 @@ import express = require('express');
 
 const app = express();
 const swaggerDocument = {
-	swagger: '2.0',
-	info: { version: '1.0.0', title: 'Example API' },
-	paths: { '/user': { get: { responses: { 200: { description: 'all users' } } } } }
+    swagger: '2.0',
+    info: { version: '1.0.0', title: 'Example API' },
+    paths: { '/user': { get: { responses: { 200: { description: 'all users' } } } } },
 };
 const swaggerDocumentSplit = swaggerDocument;
 
 const options = {
-	validatorUrl: null,
-	oauth: {
-		clientId: 'your-client-id1',
-		clientSecret: 'your-client-secret-if-required1',
-		realm: 'your-realms1',
-		appName: 'your-app-name1',
-		scopeSeparator: ',',
-		additionalQueryStringParams: {}
-	},
-	docExpansion: 'full',
+    validatorUrl: null,
+    oauth: {
+        clientId: 'your-client-id1',
+        clientSecret: 'your-client-secret-if-required1',
+        realm: 'your-realms1',
+        appName: 'your-app-name1',
+        scopeSeparator: ',',
+        additionalQueryStringParams: {},
+    },
+    docExpansion: 'full',
 };
 
 app.use('/api-docs', swaggerUi.serve);
-app.get('/api-docs', swaggerUi.setup(swaggerDocument, false, options, '.swagger-ui .topbar { background-color: red }'));
+app.get(
+    '/api-docs',
+    swaggerUi.setup(swaggerDocument, undefined, options, '.swagger-ui .topbar { background-color: red }'),
+);
 
 app.use('/api-docs-from-url', swaggerUi.serve);
-app.get('/api-docs-from-url', swaggerUi.setup(null, false, options, '.swagger-ui .topbar { background-color: red }', null, '/swagger.json'));
+app.get(
+    '/api-docs-from-url',
+    swaggerUi.setup(
+        undefined,
+        undefined,
+        options,
+        '.swagger-ui .topbar { background-color: red }',
+        undefined,
+        '/swagger.json',
+    ),
+);
 
 const swaggerUiOpts = {
-	explorer: false,
-	swaggerOptions: options,
-	customCss: '.swagger-ui .topbar { background-color: blue }'
+    explorer: false,
+    swaggerOptions: options,
+    customCss: '.swagger-ui .topbar { background-color: blue }',
 };
 
 app.use('/api-docs-using-object', swaggerUi.serve);
 app.get('/api-docs-using-object', swaggerUi.setup(swaggerDocument, swaggerUiOpts));
 
 const swaggerUiOpts2 = {
-	explorer: false,
-	swaggerOptions: options,
-	customCss: '.swagger-ui .topbar { background-color: pink }',
-	swaggerUrl: '/swagger.json',
-	customJs: '/my-custom.js',
-	operationsSorter: 'alpha'
+    explorer: false,
+    swaggerOptions: options,
+    customCss: '.swagger-ui .topbar { background-color: pink }',
+    swaggerUrl: '/swagger.json',
+    customJs: '/my-custom.js',
+    operationsSorter: 'alpha',
 };
 
 app.use('/api-docs-from-url-using-object', swaggerUi.serve);
-app.get('/api-docs-from-url-using-object', swaggerUi.setup(null, swaggerUiOpts2));
+app.get('/api-docs-from-url-using-object', swaggerUi.setup(undefined, swaggerUiOpts2));
 
 app.use('/api-docs-with-null', swaggerUi.serve);
-app.get('/api-docs-with-null', swaggerUi.setup(swaggerDocument, null, options, '.swagger-ui .topbar { background-color: orange }'));
+app.get(
+    '/api-docs-with-null',
+    swaggerUi.setup(swaggerDocument, undefined, options, '.swagger-ui .topbar { background-color: orange }'),
+);
 
 app.use('/api-docs-split', swaggerUi.serve);
-app.get('/api-docs-split', swaggerUi.setup(swaggerDocumentSplit, null, options, '.swagger-ui .topbar { background-color: orange }'));
+app.get(
+    '/api-docs-split',
+    swaggerUi.setup(swaggerDocumentSplit, undefined, options, '.swagger-ui .topbar { background-color: orange }'),
+);
 
 app.use('/api-docs-with-opts/', swaggerUi.serveWithOptions({ redirect: false }));
-app.get('/api-docs-with-opts/', swaggerUi.setup(swaggerDocumentSplit, null, options, '.swagger-ui .topbar { background-color: orange }'));
+app.get(
+    '/api-docs-with-opts/',
+    swaggerUi.setup(swaggerDocumentSplit, undefined, options, '.swagger-ui .topbar { background-color: orange }'),
+);
 
 const swaggerHtml = swaggerUi.generateHTML(swaggerDocument, swaggerUiOpts);