diff --git a/doc/source/api_microversion_dev.rst b/doc/source/api_microversion_dev.rst
index ab4d8e86f23e..079a9275ecc0 100644
--- a/doc/source/api_microversion_dev.rst
+++ b/doc/source/api_microversion_dev.rst
@@ -65,7 +65,7 @@ changed. The user contract covers many kinds of information such as:
     Example: an API previously could return 200, 400, 403, 404 and the
     change would make the API now also be allowed to return 409.
 
-    See [#f2]_ for the 403 case.
+    See [#f2]_ for the 400 and 403 cases.
 
   - changing a status code on a particular response
 
@@ -154,9 +154,10 @@ we need a microversion".
   microversion is probably needed.
 
 .. [#f2] The exception to not needing a microversion when returning a
-  previously unspecified error code is the 403 case. This is considered OK to
-  return even if previously unspecified in the code since it's implied given
-  keystone authentication can fail with a 403.
+  previously unspecified error code is the 400 and 403 cases. This is
+  considered OK to return even if previously unspecified in the code since
+  it's implied given keystone authentication can fail with a 403 and API
+  validation can fail with a 400 for invalid json request body.
 
 
 In Code