diff --git a/python/Round.py b/python/Round.py
index 312e0c1..63ff6b7 100644
--- a/python/Round.py
+++ b/python/Round.py
@@ -16,6 +16,9 @@ class Round:
 
     def __init__(self, winnerTeam, loserTeam, _map, duration, startTime, winnerSide):
 
+            if duration <= 0:
+                raise ValueError("Duration cannot be zero")
+
             self.winners     = winnerTeam
             self.losers      = loserTeam
             self.winnerSide = winnerSide
diff --git a/python/backends/eventStream.py b/python/backends/eventStream.py
index f91816e..b6b83ef 100644
--- a/python/backends/eventStream.py
+++ b/python/backends/eventStream.py
@@ -170,6 +170,10 @@ class EventSeries():
             elif type(e) == MapInformationEvent:
                 self.map = e.map
 
+        ### check if there are players in both teams ###
+        if not self.winnerTeam or not self.loserTeam:
+            raise ValueError("One of the teams was empty")
+
         ### normalize teamchanges
         toBeRemovedFromLosers  = [] # cannot change iteable during iteration
         toBeRemovedFromWinners = []