diff --git a/pylast.py b/pylast.py
index 3c043c0..4d84560 100644
--- a/pylast.py
+++ b/pylast.py
@@ -502,7 +502,7 @@ class _Network(object):
             
             for arg in additional_args:
                 
-                if tracks_to_scrobble[i][arg]:
+                if arg in tracks_to_scrobble[i] and tracks_to_scrobble[i][arg]:
                     if arg in args_map_to:
                         maps_to = args_map_to[arg]
                     else: