diff --git a/competition/serializers.py b/competition/serializers.py
index 8e9d643..1c40ee1 100644
--- a/competition/serializers.py
+++ b/competition/serializers.py
@@ -157,7 +157,7 @@ class ProblemSerializer(serializers.ModelSerializer):
     class Meta:
         model = models.Problem
         fields = '__all__'
-        read_only_fields = ['series', 'submitted', 'num_comments']
+        read_only_fields = ['submitted', 'num_comments']
 
     submitted = serializers.SerializerMethodField(
         'get_submitted')
diff --git a/competition/views.py b/competition/views.py
index ef878cd..dff464a 100644
--- a/competition/views.py
+++ b/competition/views.py
@@ -202,7 +202,8 @@ def perform_create(self, serializer):
         Volá sa pri vytvarani objektu,
         checkuju sa tu permissions, ci user vie vytvorit problem v danej sutazi
         """
-        if Problem.can_user_create(self.request.user, serializer.validated_data):
+        series = serializer.validated_data['series']
+        if series.can_user_modify(self.request.user):
             serializer.save()
         else:
             raise exceptions.PermissionDenied(