diff --git a/src/middleware/with-response-object-check.ts b/src/middleware/with-response-object-check.ts
index 9f8cae0..af5f8db 100644
--- a/src/middleware/with-response-object-check.ts
+++ b/src/middleware/with-response-object-check.ts
@@ -8,7 +8,10 @@ export const withResponseObjectCheck: Middleware<
 > = async (req, ctx, next) => {
   const rawResponse = await next(req, ctx)
 
-  if (typeof rawResponse === "object" && !(rawResponse instanceof Response)) {
+  if (
+    (typeof rawResponse === "object" && !(rawResponse instanceof Response)) ||
+    typeof rawResponse === "function"
+  ) {
     throw new Error(
       "Use ctx.json({...}) instead of returning an object directly."
     )
diff --git a/tests/errors/do-not-allow-raw-json.test.ts b/tests/errors/do-not-allow-raw-json.test.ts
index 8682796..7451c91 100644
--- a/tests/errors/do-not-allow-raw-json.test.ts
+++ b/tests/errors/do-not-allow-raw-json.test.ts
@@ -37,3 +37,39 @@ test("should throw an error when responding with raw JSON", async (t) => {
     )
   )
 })
+
+test("should throw an error when responding with a function", async (t) => {
+  const { axios } = await getTestRoute(t, {
+    globalSpec: {
+      authMiddleware: {},
+      beforeAuthMiddleware: [
+        async (req, ctx, next) => {
+          try {
+            return await next(req, ctx)
+          } catch (e: any) {
+            console.error(e)
+            return Response.json({ error: e.message }, { status: 500 })
+          }
+        },
+      ],
+    },
+    routeSpec: {
+      methods: ["GET"],
+      jsonBody: z.any(),
+      jsonResponse: z.any(),
+    },
+    routePath: "/",
+    routeFn: (req, ctx) => {
+      return (() => ({ foo: "bar" })) as any
+    },
+  })
+
+  const { data } = await axios.get("/", {
+    validateStatus: () => true,
+  })
+  t.true(
+    data.error.includes(
+      "Use ctx.json({...}) instead of returning an object directly"
+    )
+  )
+})