diff --git a/pep-0557.rst b/pep-0557.rst
index dfa0c39d8..1e425836c 100644
--- a/pep-0557.rst
+++ b/pep-0557.rst
@@ -756,6 +756,14 @@ through ``__init__`` (unless you suppress its creation).  Which
 approach is more appropriate will be application-specific, but both
 approaches are supported.
 
+Another reason for using ``InitVar`` fields is that the class author
+can control the order of ``__init__`` parameters.  This is especially
+important with regular fields and ``InitVar`` fields that have default
+values, as all fields with defaults must come after all fields without
+defaults.  A previous design had all init-only fields coming after
+regular fields.  This meant that if any field had a default value,
+then all init-only fields would have to have defaults values, too.
+
 asdict and astuple function names
 ---------------------------------