diff --git a/seminar/views.py b/seminar/views.py
index 59590bbf..eb3e0616 100644
--- a/seminar/views.py
+++ b/seminar/views.py
@@ -265,7 +265,7 @@ class CisloView(generic.DetailView):
 
         resene_problemy = Problem.objects.filter(cislo_reseni=context['cislo']).filter(typ__in=typy_skutecne_zadanych).order_by('cislo_zadani__cislo', 'kod')
 
-        problemy = sorted(list(set([r.problem for r in reseni])), key=lambda x:(0 if x.typ==Problem.TYP_ULOHA else 1, x.kod_v_rocniku))
+        problemy = sorted(set(r.problem for r in reseni), key=lambda x:(0 if x.typ==Problem.TYP_ULOHA else 1, x.kod_v_rocniku()))
         #setridi problemy podle typu a poradi zadani
         problem_index = {}
         for i in range(len(problemy)):