diff --git a/backend/api/serializers/group_serializer.py b/backend/api/serializers/group_serializer.py
index 2e8f33ed..92847e7f 100644
--- a/backend/api/serializers/group_serializer.py
+++ b/backend/api/serializers/group_serializer.py
@@ -20,6 +20,15 @@ class Meta:
         model = Group
         fields = ["id", "project", "students", "score"]
 
+    def validate(self, data):
+        # Make sure the score of the group is lower or equal to the maximum score
+        group: Group = self.instance
+
+        if "score" in data and data["score"] > group.project.max_score:
+            raise ValidationError(gettext("group.errors.score_exceeds_max"))
+
+        return data
+
 
 class StudentJoinGroupSerializer(StudentIDSerializer):
 
@@ -34,7 +43,7 @@ def validate(self, data):
 
         # Make sure the group is not already full
         if group.is_full():
-            raise serializers.ValidationError(gettext("group.errors.full"))
+            raise ValidationError(gettext("group.errors.full"))
 
         # Make sure the student is part of the course
         if not group.project.course.students.filter(id=student.id).exists():
@@ -42,7 +51,7 @@ def validate(self, data):
 
         # Make sure the student is not already in a group
         if student.is_enrolled_in_group(group.project):
-            raise serializers.ValidationError(gettext("group.errors.already_in_group"))
+            raise ValidationError(gettext("group.errors.already_in_group"))
 
         return data
 
diff --git a/backend/api/tests/test_group.py b/backend/api/tests/test_group.py
index 8f988a8e..0005626c 100644
--- a/backend/api/tests/test_group.py
+++ b/backend/api/tests/test_group.py
@@ -24,11 +24,11 @@ def create_course(name, academic_startyear, description=None, parent_course=None
     )
 
 
-def create_project(name, description, days, course, group_size=2):
+def create_project(name, description, days, course, group_size=2, max_score=20):
     """Create a Project with the given arguments."""
     deadline = timezone.now() + timedelta(days=days)
     return Project.objects.create(
-        name=name, description=description, deadline=deadline, course=course, group_size=group_size
+        name=name, description=description, deadline=deadline, course=course, group_size=group_size, max_score=max_score
     )
 
 
@@ -347,7 +347,7 @@ def test_update_score_of_group(self):
         course = create_course(name="sel2", academic_startyear=2023)
 
         project = create_project(
-            name="Project 1", description="Description 1", days=7, course=course
+            name="Project 1", description="Description 1", days=7, course=course, max_score=20
         )
 
         # Add this teacher to the course
@@ -368,6 +368,19 @@ def test_update_score_of_group(self):
         group.refresh_from_db()
         self.assertEqual(group.score, 20)
 
+        # Try to update the score of a group to a score higher than the maximum score
+        response = self.client.patch(
+            reverse("group-detail", args=[str(group.id)]),
+            {"score": 30},
+            follow=True,
+        )
+
+        self.assertEqual(response.status_code, 400)
+
+        # Make sure the score of the group is not updated
+        group.refresh_from_db()
+        self.assertEqual(group.score, 20)
+
 
 class GroupModelTestsAsStudent(APITestCase):
     def setUp(self) -> None: