diff --git a/layouts/partials/json-schema/resolve-additional-types.html b/layouts/partials/json-schema/resolve-additional-types.html
index d56edbc8..e0df56f4 100644
--- a/layouts/partials/json-schema/resolve-additional-types.html
+++ b/layouts/partials/json-schema/resolve-additional-types.html
@@ -15,6 +15,7 @@
     * required
     * enum
     * anchor: a string suitable for using as an html anchor for this object (if `anchor_base` was set, and the object has a title)
+    * additionalProperties: either nil, a boolean, or an OpenAPI schema object (https://swagger.io/specification/#schema-object).
 
   Note that the returned array may contain duplicate objects.
 
diff --git a/layouts/partials/openapi/render-object-table.html b/layouts/partials/openapi/render-object-table.html
index f41d8ffd..21a185e3 100644
--- a/layouts/partials/openapi/render-object-table.html
+++ b/layouts/partials/openapi/render-object-table.html
@@ -13,6 +13,15 @@
     In some cases (such as response body specifications) this isn't used, and
     instead properties have a `required` boolean attribute. We support this too.
 
+  * `additionalProperties`: one of
+
+    - `false` (no additional properties are permitted);
+    - `true` (additional properties pairs are permitted, with no constraints);
+    - an OpenAPI schema object [1] (additional properties are permitted, but 
+      with constraints on `property_data`); or
+    - `nil` (not specified in schema, use `true` as a default value).
+
+  [1]: https://swagger.io/specification/#schema-object
 */}}
 
 {{ $title := .title }}