diff --git a/CHANGELOG b/CHANGELOG
index ecfa91515f..ce5bbbbe38 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,5 @@
+* Unify PYSON string format
+
 Version 5.8.0 - 2020-11-02
 * Bug fixes (see mercurial logs for details)
 * Remove support for Python 3.5
diff --git a/tryton/pyson.py b/tryton/pyson.py
index 0bf9c673c1..0b28b61ddf 100644
--- a/tryton/pyson.py
+++ b/tryton/pyson.py
@@ -747,4 +747,6 @@ CONTEXT = {
     'DateTime': DateTime,
     'TimeDelta': TimeDelta,
     'Len': Len,
+    'true': True,
+    'false': False,
 }