diff --git a/css-env-1/Overview.bs b/css-env-1/Overview.bs
index 2d63b8b650ee..b0b9e172538f 100644
--- a/css-env-1/Overview.bs
+++ b/css-env-1/Overview.bs
@@ -291,6 +291,16 @@ use the ''env()'' function:
 	<dfn function>env()</dfn> = env( <<custom-ident>> <<integer [0,∞]>>*, <<declaration-value>>? )
 </pre>
 
+The ''env()'' function's [=argument grammar=] is:
+
+<pre class=prod>
+	<dfn><<env-args>></dfn> = env( <<declaration-value>>, <<declaration-value>>? )
+</pre>
+
+Like ''var()'', a bare comma can be used with nothing following it,
+indicating that the second <<declaration-value>> was passed,
+just as an empty sequence.
+
 The ''env()'' function can be used in place of any part of a value in any property on any element,
 or any part of a value in any descriptor on any [=at-rule=],
 and in several other places where CSS values are allowed.