diff --git a/pulsar/managers/util/drmaa/__init__.py b/pulsar/managers/util/drmaa/__init__.py
index cb8e872998d568e18958f9e0ef689f02ac47937b..757ed0f52fb530b41f724f8d8ae33199aa3f65ec 100644
--- a/pulsar/managers/util/drmaa/__init__.py
+++ b/pulsar/managers/util/drmaa/__init__.py
@@ -34,7 +34,7 @@ class DrmaaSession(object):
     """
     Abstraction around `drmaa` module `Session` objects.
     """
-    session_lock = threading.Semaphore(1)
+    session_lock = threading.Lock()
     session = None
 
     def __init__(self, session_constructor, **kwds):