diff --git a/lang/spec.html b/lang/spec.html
index 7a5c7456..2d921b23 100644
--- a/lang/spec.html
+++ b/lang/spec.html
@@ -5012,7 +5012,9 @@ <h4>Mapping constructor</h4>
 mapping will be constructed with its read-only bit on. If the inherent type
 makes a specific field readonly, then that field will be constructed with its
 read-only bit on. A specific-field that starts with <code>readonly</code> will
-also be constructed with its read-only bit on.
+also be constructed with its read-only bit on. The read-only bit of the
+mapping value or field will be set only after the mapping value has been fully
+constructed, including any field specified by a computed-name-field.
 </p>
 
 </section>