diff --git a/tournaments/models/group_stage.py b/tournaments/models/group_stage.py
index 2cac533..55b3631 100644
--- a/tournaments/models/group_stage.py
+++ b/tournaments/models/group_stage.py
@@ -76,8 +76,8 @@ class GroupStage(models.Model):
                     if ts1.team_registration in gs_teams and ts2.team_registration in gs_teams:
                         team1 = gs_teams[ts1.team_registration]
                         team2 = gs_teams[ts2.team_registration]
-                        team1.diff = total1 - total2
-                        team2.diff = total2 - total1
+                        team1.diff += total1 - total2
+                        team2.diff += total2 - total1
 
         if len(self.match_set.all()) == 0:
             teams = sorted(gs_teams.values(), key=lambda team: team.position)