diff --git a/src/create-with-winter-spec.ts b/src/create-with-winter-spec.ts
index 229a28c..63cdd44 100644
--- a/src/create-with-winter-spec.ts
+++ b/src/create-with-winter-spec.ts
@@ -172,6 +172,12 @@ function serializeToResponse(
   routeSpec: RouteSpec<any>,
   response: SerializableToResponse | Response
 ): Response {
+  if (typeof response === "symbol") {
+    throw new Error(
+      "Use ctx.json({...}) instead of returning a symbol directly."
+    )
+  }
+
   if (!shouldValidateResponse) {
     return "serializeToResponse" in response
       ? response.serializeToResponse(z.any())
diff --git a/src/lib/format-zod-error.ts b/src/lib/format-zod-error.ts
index cf87295..5b69691 100644
--- a/src/lib/format-zod-error.ts
+++ b/src/lib/format-zod-error.ts
@@ -11,6 +11,10 @@ const zodIssueToString = (issue: ZodIssue) => {
 }
 
 export const formatZodError = (error: ZodError): string => {
+  if (!Array.isArray(error.issues)) {
+    return error instanceof Error ? error.message : String(error)
+  }
+
   let message: string
   if (error.issues.length === 1) {
     const issue = error.issues[0]
diff --git a/tests/errors/do-not-allow-raw-json.test.ts b/tests/errors/do-not-allow-raw-json.test.ts
index 8682796..e6e6c91 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 symbol", 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 Symbol("invalid-response") as any
+    },
+  })
+
+  const { data } = await axios.get("/", {
+    validateStatus: () => true,
+  })
+  t.true(
+    data.error.includes(
+      "Use ctx.json({...}) instead of returning a symbol directly"
+    )
+  )
+})