diff --git a/pep-0538.txt b/pep-0538.txt
index b9a388b4d..ebe967db7 100644
--- a/pep-0538.txt
+++ b/pep-0538.txt
@@ -83,6 +83,21 @@ opt in to this locale coercion behaviour for the Python 3.6.x series by
 applying the necessary changes as a downstream patch.
 
 
+Implementation Notes
+====================
+
+Attempting to implement the PEP as originally accepted showed that the
+proposal to emit locale coercion and compatibility warnings by default
+simply wasn't practical (there were too many cases where previously working
+code failed *because of the warnings*, rather than because of latent locale
+handling defects in the affected code).
+
+As a result, the ``PY_WARN_ON_C_LOCALE`` config flag was removed, and replaced
+with a runtime ``PYTHONCOERCECLOCALE=warn`` environment variable setting
+that allows developers and system integrators to opt-in to receiving locale
+coercion and compatibility warnings, without emitting them by default.
+
+
 Background
 ==========