diff --git a/Demo/scripts/mboxconvert.py b/Demo/scripts/mboxconvert.py
index 5567173958b..ff7ca6ad5e3 100755
--- a/Demo/scripts/mboxconvert.py
+++ b/Demo/scripts/mboxconvert.py
@@ -40,7 +40,7 @@ def main():
 			sts = dofile(f) or sts
 			f.close()
 		else:
-			sys.stderr('%s: not found\n' % arg)
+			sys.stderr.write('%s: not found\n' % arg)
 			sts = 1
 	if sts:
 		sys.exit(sts)