diff --git a/types/pretty-bytes/index.d.ts b/types/pretty-bytes/index.d.ts
index 7cd856b4f5..5259fcb92a 100644
--- a/types/pretty-bytes/index.d.ts
+++ b/types/pretty-bytes/index.d.ts
@@ -1,8 +1,14 @@
-// Type definitions for pretty-bytes 4.0
+// Type definitions for pretty-bytes 5.1
 // Project: https://github.com/sindresorhus/pretty-bytes
 // Definitions by: York Yao <https://github.com/plantain-00>
+//                 Daniela Yassuda <https://github.com/danielasy>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
-declare function prettyBytes(bytes: number): string;
-export = prettyBytes;
-declare namespace prettyBytes { }
+declare function PrettyBytes(number: number, options?: PrettyBytes.PrettyBytesOptions): string;
+export = PrettyBytes;
+declare namespace PrettyBytes {
+    interface PrettyBytesOptions {
+        signed?: boolean;
+        locale?: boolean | string;
+    }
+}
diff --git a/types/pretty-bytes/pretty-bytes-tests.ts b/types/pretty-bytes/pretty-bytes-tests.ts
index 71745d9a1b..7aa89483bc 100644
--- a/types/pretty-bytes/pretty-bytes-tests.ts
+++ b/types/pretty-bytes/pretty-bytes-tests.ts
@@ -1,7 +1,18 @@
-import prettyBytes = require('pretty-bytes');
+import * as prettyBytes from 'pretty-bytes';
 
 prettyBytes(1337);
 // => '1.34 kB'
 
 prettyBytes(100);
 // => '100 B'
+
+// Display file size differences
+prettyBytes(42, { signed: true });
+// => '+42 B'
+
+// Localized output using German locale
+prettyBytes(1337, { locale: 'de' });
+// => '1,34 kB'
+
+// Localized output using system/browser locale
+prettyBytes(1337, { locale: true });
diff --git a/types/pretty-bytes/tsconfig.json b/types/pretty-bytes/tsconfig.json
index fd11c640b4..44e6385192 100644
--- a/types/pretty-bytes/tsconfig.json
+++ b/types/pretty-bytes/tsconfig.json
@@ -20,4 +20,4 @@
         "index.d.ts",
         "pretty-bytes-tests.ts"
     ]
-}
\ No newline at end of file
+}
diff --git a/types/pretty-bytes/tslint.json b/types/pretty-bytes/tslint.json
index e60c15844f..f93cf8562a 100644
--- a/types/pretty-bytes/tslint.json
+++ b/types/pretty-bytes/tslint.json
@@ -1,3 +1,3 @@
 {
     "extends": "dtslint/dt.json"
-}
\ No newline at end of file
+}
diff --git a/types/pretty-bytes/v4/index.d.ts b/types/pretty-bytes/v4/index.d.ts
new file mode 100644
index 0000000000..7cd856b4f5
--- /dev/null
+++ b/types/pretty-bytes/v4/index.d.ts
@@ -0,0 +1,8 @@
+// Type definitions for pretty-bytes 4.0
+// Project: https://github.com/sindresorhus/pretty-bytes
+// Definitions by: York Yao <https://github.com/plantain-00>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+
+declare function prettyBytes(bytes: number): string;
+export = prettyBytes;
+declare namespace prettyBytes { }
diff --git a/types/pretty-bytes/v4/pretty-bytes-tests.ts b/types/pretty-bytes/v4/pretty-bytes-tests.ts
new file mode 100644
index 0000000000..71745d9a1b
--- /dev/null
+++ b/types/pretty-bytes/v4/pretty-bytes-tests.ts
@@ -0,0 +1,7 @@
+import prettyBytes = require('pretty-bytes');
+
+prettyBytes(1337);
+// => '1.34 kB'
+
+prettyBytes(100);
+// => '100 B'
diff --git a/types/pretty-bytes/v4/tsconfig.json b/types/pretty-bytes/v4/tsconfig.json
new file mode 100644
index 0000000000..e23e4370ac
--- /dev/null
+++ b/types/pretty-bytes/v4/tsconfig.json
@@ -0,0 +1,26 @@
+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": true,
+        "strictFunctionTypes": true,
+        "baseUrl": "../../",
+        "typeRoots": [
+            "../../"
+        ],
+        "types": [],
+        "paths": {
+            "pretty-bytes": [ "pretty-bytes/v4" ]
+        },
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true
+    },
+    "files": [
+        "index.d.ts",
+        "pretty-bytes-tests.ts"
+    ]
+}
diff --git a/types/pretty-bytes/v4/tslint.json b/types/pretty-bytes/v4/tslint.json
new file mode 100644
index 0000000000..f93cf8562a
--- /dev/null
+++ b/types/pretty-bytes/v4/tslint.json
@@ -0,0 +1,3 @@
+{
+    "extends": "dtslint/dt.json"
+}