--- a/tests/test-diff-binary-file.t	Wed Feb 07 13:21:06 2018 +0530
+++ b/tests/test-diff-binary-file.t	Wed Feb 07 13:34:51 2018 +0530
@@ -81,7 +81,7 @@
   $ cat > writebin.py <<EOF
   > import sys
   > path = sys.argv[1]
-  > open(path, 'wb').write('\x00\x01\x02\x03')
+  > open(path, 'wb').write(b'\x00\x01\x02\x03')
   > EOF
   $ $PYTHON writebin.py binfile.bin
   $ hg add binfile.bin