diff --git a/browser.d.ts b/browser.d.ts
index 638656b2..eecfd80c 100644
--- a/browser.d.ts
+++ b/browser.d.ts
@@ -22,7 +22,7 @@ const url = 'https://upload.wikimedia.org/wikipedia/en/a/a9/Example.jpg';
 })();
 ```
 */
-export declare function fromStream(stream: ReadableStream): Promise<core.FileTypeResult>;
+export declare function fromStream(stream: ReadableStream): Promise<core.FileTypeResult | undefined>;
 
 /**
 Determine file type from a [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob).
@@ -41,7 +41,7 @@ import FileType = require('file-type/browser');
 })();
 ```
 */
-export declare function fromBlob(blob: Blob): Promise<core.FileTypeResult>;
+export declare function fromBlob(blob: Blob): Promise<core.FileTypeResult | undefined>;
 
 export {
 	fromBuffer,
diff --git a/core.d.ts b/core.d.ts
index f52526d4..ab4ec89b 100644
--- a/core.d.ts
+++ b/core.d.ts
@@ -245,12 +245,12 @@ declare namespace core {
 		/**
 		One of the supported [file types](https://github.com/sindresorhus/file-type#supported-file-types).
 		*/
-		ext: FileExtension;
+		readonly ext: FileExtension;
 
 		/**
 		The detected [MIME type](https://en.wikipedia.org/wiki/Internet_media_type).
 		*/
-		mime: MimeType;
+		readonly mime: MimeType;
 	}
 
 	type ReadableStreamWithFileType = ReadableStream & {
@@ -306,7 +306,7 @@ declare namespace core {
 	@param tokenizer - File source implementing the tokenizer interface.
 	@returns The detected file type and MIME type, or `undefined` when there is no match.
 	*/
-	function fromTokenizer(tokenizer: ITokenizer): Promise<core.FileTypeResult>;
+	function fromTokenizer(tokenizer: ITokenizer): Promise<core.FileTypeResult | undefined>;
 
 	/**
 	Deprecated: The minimum amount of bytes needed to detect a file type. Currently, it's 4100 bytes, but it can change, so don't hard-code it.
diff --git a/index.test-d.ts b/index.test-d.ts
index b3cc3930..9ecd9437 100644
--- a/index.test-d.ts
+++ b/index.test-d.ts
@@ -1,7 +1,9 @@
 import * as fs from 'fs';
 import {expectType} from 'tsd';
 import FileType = require('.');
-import {FileTypeResult, ReadableStreamWithFileType, FileExtension} from '.';
+import {FileTypeResult, ReadableStreamWithFileType, FileExtension, MimeType} from '.';
+import FileTypeBrowser = require('./browser');
+import {FileTypeResult as FileTypeResultBrowser} from './browser';
 
 expectType<Promise<FileTypeResult | undefined>>(FileType.fromBuffer(new Buffer([0xff, 0xd8, 0xff])));
 expectType<Promise<FileTypeResult | undefined>>(FileType.fromBuffer(new Uint8Array([0xff, 0xd8, 0xff])));
@@ -11,17 +13,17 @@ expectType<Promise<FileTypeResult | undefined>>(FileType.fromBuffer(new ArrayBuf
 	const result = await FileType.fromBuffer(new Buffer([0xff, 0xd8, 0xff]));
 	if (result !== undefined) {
 		expectType<FileExtension>(result.ext);
-		expectType<string>(result.mime);
+		expectType<MimeType>(result.mime);
 	}
 })();
 
 (async () => {
 	expectType<FileTypeResult | undefined>(await FileType.fromFile('myFile'));
 
-	const fileRes = await FileType.fromFile('myFile');
-	if (fileRes !== undefined) {
-		expectType<FileExtension>(fileRes.ext);
-		expectType<string>(fileRes.mime);
+	const result = await FileType.fromFile('myFile');
+	if (result !== undefined) {
+		expectType<FileExtension>(result.ext);
+		expectType<MimeType>(result.mime);
 	}
 })();
 
@@ -30,10 +32,10 @@ expectType<Promise<FileTypeResult | undefined>>(FileType.fromBuffer(new ArrayBuf
 
 	expectType<FileTypeResult | undefined>(await FileType.fromStream(stream));
 
-	const fileRes = await FileType.fromStream(stream);
-	if (fileRes !== undefined) {
-		expectType<FileExtension>(fileRes.ext);
-		expectType<string>(fileRes.mime);
+	const result = await FileType.fromStream(stream);
+	if (result !== undefined) {
+		expectType<FileExtension>(result.ext);
+		expectType<MimeType>(result.mime);
 	}
 })();
 
@@ -50,3 +52,6 @@ expectType<Promise<ReadableStreamWithFileType>>(streamWithFileType);
 (async () => {
 	expectType<FileTypeResult | undefined>((await streamWithFileType).fileType);
 })();
+
+// Browser
+expectType<Promise<FileTypeResult | undefined>>(FileTypeBrowser.fromBlob(new Blob()));
diff --git a/package.json b/package.json
index 05e1631e..ac8e5387 100644
--- a/package.json
+++ b/package.json
@@ -173,7 +173,7 @@
 		"noop-stream": "^0.1.0",
 		"pify": "^4.0.1",
 		"read-chunk": "^3.2.0",
-		"tsd": "^0.7.0",
+		"tsd": "^0.11.0",
 		"xo": "^0.25.3"
 	},
 	"dependencies": {