diff --git a/doc/go_spec.html b/doc/go_spec.html
index cb57aa301c..ed98f5375f 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1,6 +1,6 @@
 <!--{
 	"Title": "The Go Programming Language Specification - Go 1.18 Draft (incomplete)",
-	"Subtitle": "Version of Dec 13, 2021",
+	"Subtitle": "Version of Dec 16, 2021",
 	"Path": "/ref/spec"
 }-->
 
@@ -1532,7 +1532,9 @@ interface {
 <p>
 Implementation restriction:
 A union with more than one term cannot contain interface types
-with non-empty <a href="#Method_sets">method sets</a>.
+with non-empty <a href="#Method_sets">method sets</a> or which
+are or embed the <a href="#Predeclared_identifiers">predeclared identifier</a>
+<code>comparable</code>.
 </p>
 
 <p>