diff --git a/user_session_builder.py b/user_session_builder.py
index 28704f6dbd8539256ce5ab9d40bd46b0b0464409..beec0d3d092ee0a617c41e1d733dd79e290279ad 100644
--- a/user_session_builder.py
+++ b/user_session_builder.py
@@ -44,6 +44,9 @@ class User:
     ######## Private methods ########
     def __is_new_session(self, date_now):
         """Checks if a new session should be started according to the delimitation approach (see Zackay and Feitelson 2013)"""
+        
+        if len(self.sessions) == 0:
+            return True
 
         if self.delim_approach == 'arrival':
             inter_arrival_time = date_now - self.__last_submit_time