diff --git a/scripts/config.py b/scripts/config.py
index 91e37adf5..c106a97c0 100755
--- a/scripts/config.py
+++ b/scripts/config.py
@@ -7,6 +7,9 @@ Basic usage, to read the Mbed TLS or Mbed Crypto configuration:
     if 'MBEDTLS_RSA_C' in config: print('RSA is enabled')
 """
 
+# Note that the version of this script in the mbedtls-2.28 branch must remain
+# compatible with Python 3.4.
+
 ## Copyright The Mbed TLS Contributors
 ## SPDX-License-Identifier: Apache-2.0
 ##