diff --git a/css-mixins-1/Overview.bs b/css-mixins-1/Overview.bs
index b9619bad714..7693a09bacf 100644
--- a/css-mixins-1/Overview.bs
+++ b/css-mixins-1/Overview.bs
@@ -917,6 +917,9 @@ If a [=default value=] and a [=parameter type=] are both provided,
 then the default value must parse successfully according to that parameter type’s syntax.
 Otherwise, the ''@mixin'' rule is invalid.
 
+A ''@mixin'' rule cannot be a [=nested group rule=];
+it is invalid within the body of a [=style rule=].
+
 <h4 id=mixin-preamble>
 The Mixin Preamble</h4>
 
diff --git a/css-nesting-1/Overview.bs b/css-nesting-1/Overview.bs
index 352d99df07c..9c77956bd6b 100644
--- a/css-nesting-1/Overview.bs
+++ b/css-nesting-1/Overview.bs
@@ -625,7 +625,8 @@ Nesting Other At-Rules {#conditionals}
 	this specification allows <dfn export>nested group rules</dfn>
 	inside of [=style rules=]:
 	any at-rule whose body contains [=style rules=]
-	can be nested inside of a [=style rule=] as well.
+	can be nested inside of a [=style rule=] as well,
+	unless otherwise specified.
 
 	When nested in this way,
 	the contents of a [=nested group rule=]'s block