diff --git a/luigi/worker.py b/luigi/worker.py
index <HASH>..<HASH> 100644
--- a/luigi/worker.py
+++ b/luigi/worker.py
@@ -83,8 +83,6 @@ class Worker(object):
             is_complete = False
             try:
                 is_complete = task.complete()
-                if is_complete not in (True, False):
-                    raise Exception("%s.complete() returned non-boolean %r" % (task, is_complete))
             except:
                 msg = "Will not schedule %s or any dependencies due to error in complete() method:" % (task,)
                 logger.warning(msg, exc_info=1)  # like logger.exception but with WARNING level
Allowing non-boolean returns from the complete method. This should fix endsongsource and a few other sources

Change-Id: I<I>d8ef<I>c8f<I>c9fffb<I>afa<I>d0d0ea7c
Reviewed-on: <URL>