diff --git a/backend/src/services/learning-objects/learning-object-service.ts b/backend/src/services/learning-objects/learning-object-service.ts
index 1cc3cb78..6be10775 100644
--- a/backend/src/services/learning-objects/learning-object-service.ts
+++ b/backend/src/services/learning-objects/learning-object-service.ts
@@ -103,7 +103,7 @@ const learningObjectService = {
         const learningObjectRepo = getLearningObjectRepository();
         const learningObject = await learningObjectRepo.findByIdentifier(id);
         if (!learningObject) {
-            throw new NotFoundException('The specified learning object does not exist.');
+            throw new NotFoundException('learningObjectNotFound');
         }
         return learningObject.admins.map((admin) => admin.username);
     },
diff --git a/backend/src/services/learning-objects/learning-object-zip-processing-service.ts b/backend/src/services/learning-objects/learning-object-zip-processing-service.ts
index c92f456b..a0059ecc 100644
--- a/backend/src/services/learning-objects/learning-object-zip-processing-service.ts
+++ b/backend/src/services/learning-objects/learning-object-zip-processing-service.ts
@@ -68,6 +68,10 @@ function createLearningObject(metadata: LearningObjectMetadata, content: Buffer,
         callbackSchema: metadata.return_value?.callback_schema ? JSON.stringify(metadata.return_value.callback_schema) : '',
     };
 
+    if (!metadata.target_ages || metadata.target_ages.length === 0) {
+        throw new BadRequestException("errorTargetAgesMandatory");
+    }
+
     const learningObject = learningObjectRepo.create({
         admins: [],
         available: metadata.available ?? true,
diff --git a/backend/src/services/learning-paths/learning-path-service.ts b/backend/src/services/learning-paths/learning-path-service.ts
index 41dec92c..7579685a 100644
--- a/backend/src/services/learning-paths/learning-path-service.ts
+++ b/backend/src/services/learning-paths/learning-path-service.ts
@@ -150,7 +150,7 @@ const learningPathService = {
             )
         );
         if (learningObjectsOnPath.some(it => !it)) {
-            throw new BadRequestException("At least one of the specified learning objects does not exist.")
+            throw new BadRequestException("pathContainsNonExistingLearningObjects")
         }
 
         try {