diff --git a/types/normalize-url/index.d.ts b/types/normalize-url/index.d.ts
index fd76c4f72a..166477caee 100644
--- a/types/normalize-url/index.d.ts
+++ b/types/normalize-url/index.d.ts
@@ -1,4 +1,4 @@
-// Type definitions for normalize-url 3.3
+// Type definitions for normalize-url 4.1
 // Project: https://github.com/sindresorhus/normalize-url
 // Definitions by: odin3 <https://github.com/odin3>
 //                 BendingBender <https://github.com/BendingBender>
@@ -7,21 +7,154 @@
 
 declare namespace normalizeUrl {
     interface Options {
+        /**
+         * @default 'http:'
+         */
         defaultProtocol?: string;
-        forceHttp?: boolean;
-        forceHttps?: boolean;
+        /**
+         * Prepends `defaultProtocol` to the URL if it's protocol-relative.
+         *
+         * @default true
+         * @example
+         * normalizeUrl('//sindresorhus.com:80/');
+         * //=> 'http://sindresorhus.com'
+         *
+         * normalizeUrl('//sindresorhus.com:80/', {normalizeProtocol: false});
+         * //=> '//sindresorhus.com'
+         */
         normalizeProtocol?: boolean;
-        normalizeHttps?: boolean;
-        sortQueryParameters?: boolean;
-        stripFragment?: boolean;
+        /**
+         * Normalizes `https:` URLs to `http:`.
+         *
+         * @default false
+         * @example
+         * normalizeUrl('https://sindresorhus.com:80/');
+         * //=> 'https://sindresorhus.com'
+         *
+         * normalizeUrl('https://sindresorhus.com:80/', {forceHttp: true});
+         * //=> 'http://sindresorhus.com'
+         */
+        forceHttp?: boolean;
+        /**
+         * Normalizes `http:` URLs to `https:`.
+         *
+         * This option can't be used with the `forceHttp` option at the same time.
+         *
+         * @default false
+         * @example
+         * normalizeUrl('https://sindresorhus.com:80/');
+         * //=> 'https://sindresorhus.com'
+         *
+         * normalizeUrl('http://sindresorhus.com:80/', {forceHttps: true});
+         * //=> 'https://sindresorhus.com'
+         */
+        forceHttps?: boolean;
+        /**
+         * Strip the [authentication](https://en.wikipedia.org/wiki/Basic_access_authentication) part of a URL.
+         *
+         * @default true
+         * @example
+         * normalizeUrl('user:password@sindresorhus.com');
+         * //=> 'https://sindresorhus.com'
+         *
+         * normalizeUrl('user:password@sindresorhus.com', {stripAuthentication: false});
+         * //=> 'https://user:password@sindresorhus.com'
+         */
+        stripAuthentication?: boolean;
+        /**
+         * Removes hash from the URL.
+         *
+         * @default false
+         * @example
+         * normalizeUrl('sindresorhus.com/about.html#contact');
+         * //=> 'http://sindresorhus.com/about.html#contact'
+         *
+         * normalizeUrl('sindresorhus.com/about.html#contact', {stripHash: true});
+         * //=> 'http://sindresorhus.com/about.html'
+         */
         stripHash?: boolean;
+        /**
+         * Removes HTTP(S) protocol from an URL `http://sindresorhus.com` → `sindresorhus.com`.
+         *
+         * @default false
+         * @example
+         * normalizeUrl('https://sindresorhus.com');
+         * //=> 'https://sindresorhus.com'
+         *
+         * normalizeUrl('sindresorhus.com', {stripProtocol: true});
+         * //=> 'sindresorhus.com'
+         */
+        stripProtocol?: boolean;
+        /**
+         * Removes `www.` from the URL.
+         *
+         * @default true
+         * @example
+         * normalizeUrl('http://www.sindresorhus.com');
+         * //=> 'http://sindresorhus.com'
+         *
+         * normalizeUrl('http://www.sindresorhus.com', {stripWWW: false});
+         * //=> 'http://www.sindresorhus.com'
+         */
         stripWWW?: boolean;
+        /**
+         * Removes query parameters that matches any of the provided strings or regexes.
+         *
+         * @default [/^utm_\w+/i]
+         * @example
+         * normalizeUrl('www.sindresorhus.com?foo=bar&ref=test_ref', {
+         *     removeQueryParameters: ['ref']
+         * });
+         * //=> 'http://sindresorhus.com/?foo=bar'
+         */
         removeQueryParameters?: Array<RegExp | string>;
+        /**
+         * Removes trailing slash.
+         *
+         * **Note**: Trailing slash is always removed if the URL doesn't have a pathname.
+         *
+         * @default true
+         * @example
+         * normalizeUrl('http://sindresorhus.com/redirect/');
+         * //=> 'http://sindresorhus.com/redirect'
+         *
+         * normalizeUrl('http://sindresorhus.com/redirect/', {removeTrailingSlash: false});
+         * //=> 'http://sindresorhus.com/redirect/'
+         *
+         * normalizeUrl('http://sindresorhus.com/', {removeTrailingSlash: false});
+         * //=> 'http://sindresorhus.com'
+         */
         removeTrailingSlash?: boolean;
+        /**
+         * Removes the default directory index file from path that matches any of the provided strings or regexes.
+         * When `true`, the regex `/^index\.[a-z]+$/` is used.
+         *
+         * @default false
+         * @example
+         * normalizeUrl('www.sindresorhus.com/foo/default.php', {
+         *     removeDirectoryIndex: [/^default\.[a-z]+$/]
+         * });
+         * //=> 'http://sindresorhus.com/foo'
+         */
         removeDirectoryIndex?: Array<RegExp | string>;
+        /**
+         * Sorts the query parameters alphabetically by key.
+         *
+         * @default true
+         * @example
+         * normalizeUrl('www.sindresorhus.com?b=two&a=one&c=three', {
+         *     sortQueryParameters: false
+         * });
+         * //=> 'http://sindresorhus.com/?b=two&a=one&c=three'
+         */
+        sortQueryParameters?: boolean;
     }
 }
 
+/**
+ * [Normalize](https://en.wikipedia.org/wiki/URL_normalization) a URL.
+ * @param url URL to normalize.
+ */
 declare function normalizeUrl(url: string, options?: normalizeUrl.Options): string;
 
 export = normalizeUrl;
diff --git a/types/normalize-url/normalize-url-tests.ts b/types/normalize-url/normalize-url-tests.ts
index 961be30c0d..cdd87e42df 100644
--- a/types/normalize-url/normalize-url-tests.ts
+++ b/types/normalize-url/normalize-url-tests.ts
@@ -1,17 +1,23 @@
 import normalizeUrl = require('normalize-url');
 
-let str: string;
-str = normalizeUrl('sindresorhus.com');
-str = normalizeUrl('HTTP://xn--xample-hva.com:80/?b=bar&a=foo');
+normalizeUrl('sindresorhus.com'); // $ExpectType string
+normalizeUrl('HTTP://xn--xample-hva.com:80/?b=bar&a=foo'); // $ExpectType string
 
-normalizeUrl('//sindresorhus.com:80/', {normalizeProtocol: false});
-normalizeUrl('https://sindresorhus.com:80/', {normalizeHttps: true});
-normalizeUrl('sindresorhus.com/about.html#contact', {stripFragment: false});
-normalizeUrl('http://www.sindresorhus.com/about.html#contact', {stripWWW: false});
+normalizeUrl('//sindresorhus.com:80/', { defaultProtocol: 'https:' });
+normalizeUrl('//sindresorhus.com:80/', { normalizeProtocol: false });
+normalizeUrl('https://sindresorhus.com:80/', { forceHttp: true });
+normalizeUrl('http://sindresorhus.com:80/', { forceHttps: true });
+normalizeUrl('user:password@sindresorhus.com', { stripAuthentication: false });
+normalizeUrl('sindresorhus.com/about.html#contact', { stripHash: true });
+normalizeUrl('https://sindresorhus.com', { stripProtocol: true });
+normalizeUrl('http://www.sindresorhus.com', { stripWWW: false });
 normalizeUrl('www.sindresorhus.com?foo=bar&ref=test_ref', {
-    removeQueryParameters: ['ref', /test/]
+    removeQueryParameters: ['ref', /test/],
 });
-normalizeUrl('http://sindresorhus.com/', {removeTrailingSlash: false});
+normalizeUrl('http://sindresorhus.com/', { removeTrailingSlash: false });
 normalizeUrl('www.sindresorhus.com/foo/default.php', {
-    removeDirectoryIndex: [/^default\.[a-z]+$/, 'foo']
+    removeDirectoryIndex: [/^default\.[a-z]+$/, 'foo'],
+});
+normalizeUrl('www.sindresorhus.com?b=two&a=one&c=three', {
+    sortQueryParameters: false,
 });
diff --git a/types/normalize-url/tsconfig.json b/types/normalize-url/tsconfig.json
index 1626fe81b7..0f18de6c48 100644
--- a/types/normalize-url/tsconfig.json
+++ b/types/normalize-url/tsconfig.json
@@ -6,7 +6,7 @@
         ],
         "noImplicitAny": true,
         "noImplicitThis": true,
-        "strictNullChecks": false,
+        "strictNullChecks": true,
         "strictFunctionTypes": true,
         "baseUrl": "../",
         "typeRoots": [
@@ -20,4 +20,4 @@
         "index.d.ts",
         "normalize-url-tests.ts"
     ]
-}
\ No newline at end of file
+}
diff --git a/types/normalize-url/tslint.json b/types/normalize-url/tslint.json
index 279473e356..f93cf8562a 100644
--- a/types/normalize-url/tslint.json
+++ b/types/normalize-url/tslint.json
@@ -1,7 +1,3 @@
 {
-    "extends": "dtslint/dt.json",
-    "rules": {
-        // This package uses the Function type, and it will take effort to fix.
-        "ban-types": false
-    }
+    "extends": "dtslint/dt.json"
 }
diff --git a/types/normalize-url/v3/index.d.ts b/types/normalize-url/v3/index.d.ts
new file mode 100644
index 0000000000..fd76c4f72a
--- /dev/null
+++ b/types/normalize-url/v3/index.d.ts
@@ -0,0 +1,27 @@
+// Type definitions for normalize-url 3.3
+// Project: https://github.com/sindresorhus/normalize-url
+// Definitions by: odin3 <https://github.com/odin3>
+//                 BendingBender <https://github.com/BendingBender>
+//                 Mathieu M-Gosselin <https://github.com/mathieumg>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+
+declare namespace normalizeUrl {
+    interface Options {
+        defaultProtocol?: string;
+        forceHttp?: boolean;
+        forceHttps?: boolean;
+        normalizeProtocol?: boolean;
+        normalizeHttps?: boolean;
+        sortQueryParameters?: boolean;
+        stripFragment?: boolean;
+        stripHash?: boolean;
+        stripWWW?: boolean;
+        removeQueryParameters?: Array<RegExp | string>;
+        removeTrailingSlash?: boolean;
+        removeDirectoryIndex?: Array<RegExp | string>;
+    }
+}
+
+declare function normalizeUrl(url: string, options?: normalizeUrl.Options): string;
+
+export = normalizeUrl;
diff --git a/types/normalize-url/v3/normalize-url-tests.ts b/types/normalize-url/v3/normalize-url-tests.ts
new file mode 100644
index 0000000000..961be30c0d
--- /dev/null
+++ b/types/normalize-url/v3/normalize-url-tests.ts
@@ -0,0 +1,17 @@
+import normalizeUrl = require('normalize-url');
+
+let str: string;
+str = normalizeUrl('sindresorhus.com');
+str = normalizeUrl('HTTP://xn--xample-hva.com:80/?b=bar&a=foo');
+
+normalizeUrl('//sindresorhus.com:80/', {normalizeProtocol: false});
+normalizeUrl('https://sindresorhus.com:80/', {normalizeHttps: true});
+normalizeUrl('sindresorhus.com/about.html#contact', {stripFragment: false});
+normalizeUrl('http://www.sindresorhus.com/about.html#contact', {stripWWW: false});
+normalizeUrl('www.sindresorhus.com?foo=bar&ref=test_ref', {
+    removeQueryParameters: ['ref', /test/]
+});
+normalizeUrl('http://sindresorhus.com/', {removeTrailingSlash: false});
+normalizeUrl('www.sindresorhus.com/foo/default.php', {
+    removeDirectoryIndex: [/^default\.[a-z]+$/, 'foo']
+});
diff --git a/types/normalize-url/v3/tsconfig.json b/types/normalize-url/v3/tsconfig.json
new file mode 100644
index 0000000000..dda934378d
--- /dev/null
+++ b/types/normalize-url/v3/tsconfig.json
@@ -0,0 +1,28 @@
+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": false,
+        "strictFunctionTypes": true,
+        "baseUrl": "../../",
+        "typeRoots": [
+            "../../"
+        ],
+        "paths": {
+            "normalize-url": [
+                "normalize-url/v3"
+            ]
+        },
+        "types": [],
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "files": [
+        "index.d.ts",
+        "normalize-url-tests.ts"
+    ]
+}
diff --git a/types/normalize-url/v3/tslint.json b/types/normalize-url/v3/tslint.json
new file mode 100644
index 0000000000..f93cf8562a
--- /dev/null
+++ b/types/normalize-url/v3/tslint.json
@@ -0,0 +1,3 @@
+{
+    "extends": "dtslint/dt.json"
+}