diff --git a/backend/src/app.ts b/backend/src/app.ts
index cd0e715b..b21bb9f1 100644
--- a/backend/src/app.ts
+++ b/backend/src/app.ts
@@ -6,13 +6,13 @@ import themeRoutes from './routes/themes.js';
 import learningPathRoutes from './routes/learningPaths.js';
 import learningObjectRoutes from './routes/learningObjects.js';
 
-import studentRouter from './routes/student';
-import groupRouter from './routes/group';
-import assignmentRouter from './routes/assignment';
-import submissionRouter from './routes/submission';
-import classRouter from './routes/class';
-import questionRouter from './routes/question';
-import loginRouter from './routes/login';
+import studentRouter from './routes/student.js';
+import groupRouter from './routes/group.js';
+import assignmentRouter from './routes/assignment.js';
+import submissionRouter from './routes/submission.js';
+import classRouter from './routes/class.js';
+import questionRouter from './routes/question.js';
+import loginRouter from './routes/login.js';
 
 const app: Express = express();
 const port: string | number = getNumericEnvVar(EnvVars.Port);
diff --git a/backend/src/controllers/learningObjects.ts b/backend/src/controllers/learningObjects.ts
index 2d733d97..d0df24fd 100644
--- a/backend/src/controllers/learningObjects.ts
+++ b/backend/src/controllers/learningObjects.ts
@@ -1,6 +1,6 @@
 import { Request, Response } from 'express';
 import { getLearningObjectsFromPath } from '../services/learningObjects.js';
-import { FALLBACK_LANG } from '../config';
+import { FALLBACK_LANG } from '../config.js';
 
 export async function getAllLearningObjects(
     req: Request,
diff --git a/backend/src/controllers/themes.ts b/backend/src/controllers/themes.ts
index 62564485..817464ab 100644
--- a/backend/src/controllers/themes.ts
+++ b/backend/src/controllers/themes.ts
@@ -3,7 +3,7 @@ import path from 'path';
 import yaml from 'js-yaml';
 import { Request, Response } from 'express';
 import { themes } from '../data/themes.js';
-import { FALLBACK_LANG } from '../config';
+import { FALLBACK_LANG } from '../config.js';
 
 interface Translations {
     curricula_page: {