diff --git a/pyx12/scripts/x12norm.py b/pyx12/scripts/x12norm.py
index 4dfa8fdc..543758ff 100755
--- a/pyx12/scripts/x12norm.py
+++ b/pyx12/scripts/x12norm.py
@@ -52,7 +52,7 @@ def main():
         if not os.path.isfile(file_in):
             logger.error('Could not open file "%s"' % (file_in))
 
-        fd_out = tempfile.TemporaryFile()
+        fd_out = tempfile.TemporaryFile(mode='w')
         src = pyx12.x12file.X12Reader(file_in)
         for seg_data in src:
             if args.fixcounting: