diff --git a/castor/scheduler/diskmanager/runningtransfersset.py b/castor/scheduler/diskmanager/runningtransfersset.py
index 7f9aecbe6cab995468576dd61611a73a8a629cd8..93be00b44f1f9f14fecec23689cbdaa3b2c1f4af 100644
--- a/castor/scheduler/diskmanager/runningtransfersset.py
+++ b/castor/scheduler/diskmanager/runningtransfersset.py
@@ -166,7 +166,7 @@ class RunningTransfersSet(object):
         if t.transferId == transferid:
           return t
     finally:
-      self.tapelock.acquire()
+      self.tapelock.release()
     raise KeyError
 
   def setProcess(self, transferid, process):