diff --git a/VMDKstream.py b/VMDKstream.py
index 26262b5..56ed009 100755
--- a/VMDKstream.py
+++ b/VMDKstream.py
@@ -79,8 +79,8 @@ def __str__(self):
 ddb.virtualHWVersion = "7"'''
 
 
-def create_sparse_header(inFileSectors = None, descriptorOffset = 1,
-                         descriptorSize = None, gdOffset = 0xFFFFFFFFFFFFFFFF):
+def create_sparse_header(inFileSectors, descriptorSize,
+                         gdOffset = 0xFFFFFFFFFFFFFFFF):
     # While theoretically variable we set these based on current VMWare
     # convention
     grainSize = 128
@@ -88,6 +88,8 @@ def create_sparse_header(inFileSectors = None, descriptorOffset = 1,
     overHead = 128
     formatVersion = 3 # NOTE: Conflicts with VMWare docs - determined by trial/error
 
+    descriptorOffset = 1
+
     # The following are always fixed in the "stream-optimized" format we are
     # creating
     compressAlgorithm = 1