diff --git a/core/src/init.js b/core/src/init.js
index 9e10a6941e1..1bcd8218702 100644
--- a/core/src/init.js
+++ b/core/src/init.js
@@ -8,8 +8,8 @@ import _ from 'underscore'
 import $ from 'jquery'
 import moment from 'moment'
 
-import { initSessionHeartBeat } from './session-heartbeat.js'
 import OC from './OC/index.js'
+import { initSessionHeartBeat } from './session-heartbeat.ts'
 import { setUp as setUpContactsMenu } from './components/ContactsMenu.js'
 import { setUp as setUpMainMenu } from './components/MainMenu.js'
 import { setUp as setUpUserMenu } from './components/UserMenu.js'
diff --git a/core/src/session-heartbeat.js b/core/src/session-heartbeat.ts
similarity index 100%
rename from core/src/session-heartbeat.js
rename to core/src/session-heartbeat.ts