diff --git a/index.bs b/index.bs
index 46c95ea..462bf60 100644
--- a/index.bs
+++ b/index.bs
@@ -108,6 +108,7 @@ spec: ECMASCRIPT; urlPrefix: https://tc39.es/ecma262/
   type: dfn
     text: surrounding agent; url: surrounding-agent
     text: agent cluster; url: sec-agent-clusters
+    text: is not an object; url: sec-object-type
 </pre>
 
 <h2 id="intro">Introduction</h2>
@@ -607,7 +608,7 @@ The {{ModelContext}} interface provides methods for web applications to register
 interface ModelContext : EventTarget {
   Promise<undefined> registerTool(ModelContextTool tool, optional ModelContextRegisterToolOptions options = {});
   Promise<sequence<RegisteredTool>> getTools(optional ModelContextGetToolOptions options = {});
-  Promise<DOMString> executeTool(RegisteredTool tool, optional object inputObject = {}, optional ModelContextExecuteToolOptions options = {});
+  Promise<DOMString> executeTool(RegisteredTool tool, optional any inputObject, optional ModelContextExecuteToolOptions options = {});
 
   attribute EventHandler ontoolchange;
 };
@@ -927,6 +928,8 @@ The <dfn method for=ModelContext>executeTool(<var>tool</var>, <var>inputObject</
 
 1. [=Assert=]: |expectedTargetOrigin| is not an [=opaque origin=].
 
+1. If |inputObject| [=is not an Object=], then return [=a promise rejected with=] a {{TypeError}}.
+
 1. Let |inputArguments| be the result of [=serializing a JavaScript value to a JSON string=] given
    |inputObject|. If this threw an exception, then return [=a promise rejected with=] that exception.