diff --git a/src/middleware/http-exceptions.ts b/src/middleware/http-exceptions.ts
index 9e0f658..fa68d00 100644
--- a/src/middleware/http-exceptions.ts
+++ b/src/middleware/http-exceptions.ts
@@ -70,3 +70,9 @@ export class ResponseValidationError extends WinterSpecMiddlewareError {
     super(formatZodError(error), 500)
   }
 }
+
+export class ResponseObjectNotAllowedError extends WinterSpecMiddlewareError {
+  constructor() {
+    super("Use ctx.json({...}) instead of returning an object directly.", 500)
+  }
+}
diff --git a/src/middleware/with-response-object-check.ts b/src/middleware/with-response-object-check.ts
index 9f8cae0..25b3a37 100644
--- a/src/middleware/with-response-object-check.ts
+++ b/src/middleware/with-response-object-check.ts
@@ -1,4 +1,4 @@
-import { ResponseValidationError } from "./http-exceptions.js"
+import { ResponseObjectNotAllowedError } from "./http-exceptions.js"
 import { Middleware } from "./types.js"
 import { RouteSpec } from "src/types/route-spec.js"
 
@@ -9,9 +9,7 @@ export const withResponseObjectCheck: Middleware<
   const rawResponse = await next(req, ctx)
 
   if (typeof rawResponse === "object" && !(rawResponse instanceof Response)) {
-    throw new Error(
-      "Use ctx.json({...}) instead of returning an object directly."
-    )
+    throw new ResponseObjectNotAllowedError()
   }
 
   return rawResponse
diff --git a/tests/middleware/with-response-object-check.test.ts b/tests/middleware/with-response-object-check.test.ts
new file mode 100644
index 0000000..bba30d0
--- /dev/null
+++ b/tests/middleware/with-response-object-check.test.ts
@@ -0,0 +1,39 @@
+import test from "ava"
+import { z } from "zod"
+import { getTestRoute } from "../fixtures/get-test-route.js"
+import { createWithDefaultExceptionHandling } from "../../src/middleware/with-default-exception-handling.js"
+
+test("returning a plain object with jsonResponse validation under default exception handling", async (t) => {
+  const { axios } = await getTestRoute(t, {
+    globalSpec: {
+      authMiddleware: {},
+      beforeAuthMiddleware: [createWithDefaultExceptionHandling()],
+    },
+    routeSpec: {
+      auth: "none",
+      methods: ["GET"],
+      jsonResponse: z.object({
+        ok: z.boolean(),
+        message: z.string(),
+      }),
+    },
+    routeFn: (_, ctx) => {
+      // Accidental plain object return
+      return { ok: true, message: "hello" } as any
+    },
+    routePath: "/test-plain-object",
+  })
+
+  const response = await axios.get("/test-plain-object", {
+    validateStatus: () => true,
+  })
+
+  console.log("Response status:", response.status)
+  console.log("Response data:", response.data)
+
+  t.is(response.status, 500)
+  t.is(
+    response.data.message,
+    "Use ctx.json({...}) instead of returning an object directly."
+  )
+})