diff --git a/lib/fileio.py b/lib/fileio.py
index 7651930..83f78eb 100644
--- a/lib/fileio.py
+++ b/lib/fileio.py
@@ -182,7 +182,7 @@ def addBlockToNifti(fname, block, blockInds,dim=None,volInd=None,aff=None,hdr=No
     while fileLocked:
         try:
             # Create lock file, so other jobs know we are writing to this file
-            os.open(fname + ".lock", os.O_CREAT|os.O_EXCL|os.O_RDWR)
+            f=os.open(fname + ".lock", os.O_CREAT|os.O_EXCL|os.O_RDWR)
             fileLocked = False
         except FileExistsError:
             fileLocked = True