diff --git a/src/calibre/utils/ipc/worker.py b/src/calibre/utils/ipc/worker.py
index fa512c56ba..f2368bb495 100644
--- a/src/calibre/utils/ipc/worker.py
+++ b/src/calibre/utils/ipc/worker.py
@@ -55,7 +55,7 @@ PARALLEL_FUNCS = {
       ('calibre.utils.ipc.worker', 'arbitrary', None),
 
       'arbitrary_n' :
-      ('calibre.utils.ipc.worker', 'arbitrary', 'notification'),
+      ('calibre.utils.ipc.worker', 'arbitrary_n', 'notification'),
 }
 
 class Progress(Thread):