diff --git a/multi_user/preferences.py b/multi_user/preferences.py
index 388fe86..dde880f 100644
--- a/multi_user/preferences.py
+++ b/multi_user/preferences.py
@@ -100,7 +100,13 @@ def set_log_level(self, value):
     logging.getLogger().setLevel(value)
 
 def set_active_replay(self, value):
-    max_index = len(bpy.context.window_manager.session.replay_files)-1
+    files_count = len(bpy.context.window_manager.session.replay_files)
+
+    if files_count == 0:
+        return
+
+    max_index = files_count-1
+
     if value > max_index:
         value = max_index