diff --git a/src/server/mcp.test.ts b/src/server/mcp.test.ts
index 49f852d6..fd71443d 100644
--- a/src/server/mcp.test.ts
+++ b/src/server/mcp.test.ts
@@ -265,6 +265,7 @@ describe("tool()", () => {
     expect(result.tools[0].name).toBe("test");
     expect(result.tools[0].inputSchema).toEqual({
       type: "object",
+      properties: {},
     });
 
     // Adding the tool before the connection was established means no notification was sent
diff --git a/src/server/mcp.ts b/src/server/mcp.ts
index 5b864b8b..436a948f 100644
--- a/src/server/mcp.ts
+++ b/src/server/mcp.ts
@@ -1018,6 +1018,7 @@ export type RegisteredTool = {
 
 const EMPTY_OBJECT_JSON_SCHEMA = {
   type: "object" as const,
+  properties: {},
 };
 
 // Helper to check if an object is a Zod schema (ZodRawShape)