diff --git a/models/f_room.py b/models/f_room.py
index fb6f7d35f278907c8fbfcf12c8b1df0ec6499739..5842d09a29da98cf3168c524cd90bfc751afa977 100644
--- a/models/f_room.py
+++ b/models/f_room.py
@@ -9,7 +9,7 @@ db.define_table(
     Field('creation', 'datetime', default=request.now, notnull=True),
     Field('heartbeat', 'datetime', default=request.now, notnull=True),
     Field('started', 'boolean', default=False),
-    Field('roles', 'string', default="", notnull=True),
+    Field('roles', 'string', default="{}", notnull=True),
     Field('closed', 'boolean', default=False)
 )