diff --git a/src/utils/KeyVerificationStateObserver.js b/src/utils/KeyVerificationStateObserver.ts
similarity index 86%
rename from src/utils/KeyVerificationStateObserver.js
rename to src/utils/KeyVerificationStateObserver.ts
index 023cdf3a75..e4fae3f3c8 100644
--- a/src/utils/KeyVerificationStateObserver.js
+++ b/src/utils/KeyVerificationStateObserver.ts
@@ -17,14 +17,14 @@ limitations under the License.
 import { MatrixClientPeg } from '../MatrixClientPeg';
 import { _t } from '../languageHandler';
 
-export function getNameForEventRoom(userId, roomId) {
+export function getNameForEventRoom(userId: string, roomId: string): string {
     const client = MatrixClientPeg.get();
     const room = client.getRoom(roomId);
     const member = room && room.getMember(userId);
     return member ? member.name : userId;
 }
 
-export function userLabelForEventRoom(userId, roomId) {
+export function userLabelForEventRoom(userId: string, roomId: string): string {
     const name = getNameForEventRoom(userId, roomId);
     if (name !== userId) {
         return _t("%(name)s (%(userId)s)", { name, userId });