diff --git a/src/domain/session/room/timeline/MessageBody.js b/src/domain/session/room/timeline/MessageBody.js
index 65b487a9..f2df1166 100644
--- a/src/domain/session/room/timeline/MessageBody.js
+++ b/src/domain/session/room/timeline/MessageBody.js
@@ -1,4 +1,4 @@
-import { linkify } from "./linkify/linkify.js";
+import { linkify } from "./linkify/linkify";
 import { getIdentifierColorNumber, avatarInitials } from "../../../avatar";
 
 /**
diff --git a/src/domain/session/room/timeline/deserialize.js b/src/domain/session/room/timeline/deserialize.js
index b59c2e59..2e2a30f2 100644
--- a/src/domain/session/room/timeline/deserialize.js
+++ b/src/domain/session/room/timeline/deserialize.js
@@ -15,7 +15,7 @@ limitations under the License.
 */
 
 import { MessageBody, HeaderBlock, TableBlock, ListBlock, CodeBlock, PillPart, FormatPart, NewLinePart, RulePart, TextPart, LinkPart, ImagePart } from "./MessageBody.js"
-import { linkify } from "./linkify/linkify.js";
+import {linkify} from "./linkify/linkify";
 
 /* At the time of writing (Jul 1 2021), Matrix Spec recommends
  * allowing the following HTML tags:
diff --git a/src/domain/session/room/timeline/linkify/linkify.js b/src/domain/session/room/timeline/linkify/linkify.ts
similarity index 77%
rename from src/domain/session/room/timeline/linkify/linkify.js
rename to src/domain/session/room/timeline/linkify/linkify.ts
index 6c285d79..6e5f90d1 100644
--- a/src/domain/session/room/timeline/linkify/linkify.js
+++ b/src/domain/session/room/timeline/linkify/linkify.ts
@@ -21,10 +21,8 @@ import { regex } from "./regex.js";
  * For each such separated token, callback is called
  * with the token and a boolean passed as argument.
  * The boolean indicates whether the token is a link or not.
- * @param {string} text Text to split
- * @param {function(string, boolean)} callback A function to call with split tokens
  */
-export function linkify(text, callback) {
+export function linkify(text: string, callback: (token: string, isLink: boolean) => void): void {
     const matches = text.matchAll(regex);
     let curr = 0;
     for (let match of matches) {
@@ -32,16 +30,18 @@ export function linkify(text, callback) {
         callback(precedingText, false);
         callback(match[0], true);
         const len = match[0].length;
-        curr = match.index + len;
+        curr = match.index! + len;
     }
     const remainingText = text.slice(curr);
     callback(remainingText, false);
 }
 
-export function tests() {
+export function tests(): any {
 
     class MockCallback {
-        mockCallback(text, isLink) {
+        result: { type: "link" | "text", text: string }[];
+
+        mockCallback(text: string, isLink: boolean): void {
             if (!text.length) {
                 return;
             }
@@ -53,13 +53,13 @@ export function tests() {
         }
     }
 
-    function test(assert, input, output) {
+    function test(assert, input, output): void {
         const m = new MockCallback;
         linkify(input, m.mockCallback.bind(m));
         assert.deepEqual(output, m.result);
     }
 
-    function testLink(assert, link, expectFail = false) {
+    function testLink(assert, link, expectFail = false): void {
         const input = link;
         const output = expectFail ? [{ type: "text", text: input }] :
             [{ type: "link", text: input }];
@@ -67,23 +67,23 @@ export function tests() {
     }
 
     return {
-        "Link with host": assert => {
+        "Link with host": (assert): void => {
             testLink(assert, "https://matrix.org");
         },
 
-        "Link with host & path": assert => {
+        "Link with host & path": (assert): void => {
             testLink(assert, "https://matrix.org/docs/develop");
         },
 
-        "Link with host & fragment": assert => {
+        "Link with host & fragment": (assert): void => {
             testLink(assert, "https://matrix.org#test");
         },
 
-        "Link with host & query": assert => {
+        "Link with host & query": (assert): void => {
             testLink(assert, "https://matrix.org/?foo=bar");
         },
 
-        "Complex link": assert => {
+        "Complex link": (assert): void => {
             const link = "https://www.foobar.com/url?sa=t&rct=j&q=&esrc=s&source" +
                 "=web&cd=&cad=rja&uact=8&ved=2ahUKEwjyu7DJ-LHwAhUQyzgGHc" +
                 "OKA70QFjAAegQIBBAD&url=https%3A%2F%2Fmatrix.org%2Fdocs%" +
@@ -92,26 +92,26 @@ export function tests() {
             testLink(assert, link);
         },
 
-        "Localhost link": assert => {
+        "Localhost link": (assert): void => {
             testLink(assert, "http://localhost");
             testLink(assert, "http://localhost:3000");
         },
 
-        "IPV4 link": assert => {
+        "IPV4 link": (assert): void => {
             testLink(assert, "https://192.0.0.1");
             testLink(assert, "https://250.123.67.23:5924");
         },
 
-        "IPV6 link": assert => {
+        "IPV6 link": (assert): void => {
             testLink(assert, "http://[2001:0db8:85a3:0000:0000:8a2e:0370:7334]");
             testLink(assert, "http://[2001:0db8:85a3:0000:0000:8a2e:0370:7334]:7000");
         },
 
-        "Missing scheme must not linkify": assert => {
+        "Missing scheme must not linkify": (assert): void => {
             testLink(assert, "matrix.org/foo/bar", true);
         },
 
-        "Punctuation at end of link must not linkify": assert => {
+        "Punctuation at end of link must not linkify": (assert): void => {
             const link = "https://foo.bar/?nenjil=lal810";
             const end = ".,? ";
             for (const char of end) {
@@ -120,28 +120,28 @@ export function tests() {
             }
         },
 
-        "Link doesn't adopt closing parenthesis": assert => {
+        "Link doesn't adopt closing parenthesis": (assert): void => {
             const link = "(https://matrix.org)";
             const out = [{ type: "text", text: "(" }, { type: "link", text: "https://matrix.org" }, { type: "text", text: ")" }];
             test(assert, link, out);
         },
 
-        "Unicode in hostname must not linkify": assert => {
+        "Unicode in hostname must not linkify": (assert): void => {
             const link = "https://foo.bar\uD83D\uDE03.com";
             const out = [{ type: "link", text: "https://foo.bar" },
             { type: "text", text: "\uD83D\uDE03.com" }];
             test(assert, link, out);
         },
 
-        "Link with unicode only after / must linkify": assert => {
+        "Link with unicode only after / must linkify": (assert): void => {
             testLink(assert, "https://foo.bar.com/\uD83D\uDE03");
         },
 
-        "Link with unicode after fragment without path must linkify": assert => {
+        "Link with unicode after fragment without path must linkify": (assert): void => {
             testLink(assert, "https://foo.bar.com#\uD83D\uDE03");
         },
 
-        "Link ends with <": assert => {
+        "Link ends with <": (assert): void => {
             const link = "https://matrix.org<";
             const out = [{ type: "link", text: "https://matrix.org" }, { type: "text", text: "<" }];
             test(assert, link, out);
diff --git a/src/domain/session/room/timeline/linkify/regex.js b/src/domain/session/room/timeline/linkify/regex.ts
similarity index 100%
rename from src/domain/session/room/timeline/linkify/regex.js
rename to src/domain/session/room/timeline/linkify/regex.ts