diff --git a/packages/coding-agent/src/tools/submit-result.ts b/packages/coding-agent/src/tools/submit-result.ts
index 752223702..d8e64a54b 100644
--- a/packages/coding-agent/src/tools/submit-result.ts
+++ b/packages/coding-agent/src/tools/submit-result.ts
@@ -89,7 +89,7 @@ export class SubmitResultTool implements AgentTool<TObject, SubmitResultDetails>
 					...(normalizedSchema as object),
 					description: `Structured output matching the schema:\n${schemaHint}`,
 				})
-			: Type.Any({ description: "Structured JSON output (no schema specified)" });
+			: Type.Object({}, { additionalProperties: true, description: "Structured JSON output (no schema specified)" });
 
 		this.parameters = Type.Object({
 			data: Type.Optional(dataSchema),