diff --git a/sources/29-web2py-english/09.markmin b/sources/29-web2py-english/09.markmin
index 5598afdf..a56531b6 100644
--- a/sources/29-web2py-english/09.markmin
+++ b/sources/29-web2py-english/09.markmin
@@ -922,6 +922,8 @@ def verify_otp(user, otp):
   for t in range(time_start - 1, time_end + 1):
      to_hash = str(t) + user.motp_secret + user.motp_pin
      hash = md5(to_hash).hexdigest()[:6]
+     # Comment the previous line and uncomment the next line if using Python 3.
+     # hash = md5(to_hash.encode(encoding='utf8')).hexdigest()[:6]
      if otp == hash:
        return hash