diff --git a/src/context.ts b/src/context.ts
index acd18389..a24fa26d 100644
--- a/src/context.ts
+++ b/src/context.ts
@@ -11,7 +11,13 @@ import type {
 } from './types'
 import { HtmlEscapedCallbackPhase, resolveCallback } from './utils/html'
 import type { RedirectStatusCode, StatusCode } from './utils/http-status'
-import type { IsAny, JSONParsed, JSONValue, SimplifyDeepArray } from './utils/types'
+import type {
+  InvalidJSONValue,
+  IsAny,
+  JSONParsed,
+  JSONValue,
+  SimplifyDeepArray,
+} from './utils/types'
 
 type HeaderRecord = Record<string, string | string[]>
 
@@ -142,12 +148,18 @@ interface TextRespond {
  * @returns {JSONRespondReturn<T, U>} - The response after rendering the JSON object, typed with the provided object and status code types.
  */
 interface JSONRespond {
-  <T extends JSONValue | SimplifyDeepArray<unknown>, U extends StatusCode = StatusCode>(
+  <
+    T extends JSONValue | SimplifyDeepArray<unknown> | InvalidJSONValue,
+    U extends StatusCode = StatusCode
+  >(
     object: T,
     status?: U,
     headers?: HeaderRecord
   ): JSONRespondReturn<T, U>
-  <T extends JSONValue | SimplifyDeepArray<unknown>, U extends StatusCode = StatusCode>(
+  <
+    T extends JSONValue | SimplifyDeepArray<unknown> | InvalidJSONValue,
+    U extends StatusCode = StatusCode
+  >(
     object: T,
     init?: ResponseInit
   ): JSONRespondReturn<T, U>
@@ -160,7 +172,7 @@ interface JSONRespond {
  * @returns {Response & TypedResponse<SimplifyDeepArray<T> extends JSONValue ? (JSONValue extends SimplifyDeepArray<T> ? never : JSONParsed<T>) : never, U, 'json'>} - The response after rendering the JSON object, typed with the provided object and status code types.
  */
 type JSONRespondReturn<
-  T extends JSONValue | SimplifyDeepArray<unknown>,
+  T extends JSONValue | SimplifyDeepArray<unknown> | InvalidJSONValue,
   U extends StatusCode
 > = Response &
   TypedResponse<
@@ -168,7 +180,7 @@ type JSONRespondReturn<
       ? JSONValue extends SimplifyDeepArray<T>
         ? never
         : JSONParsed<T>
-      : never,
+      : JSONParsed<T>,
     U,
     'json'
   >
@@ -692,7 +704,7 @@ export class Context<
    * ```
    */
   json: JSONRespond = <
-    T extends JSONValue | SimplifyDeepArray<unknown>,
+    T extends JSONValue | SimplifyDeepArray<unknown> | InvalidJSONValue,
     U extends StatusCode = StatusCode
   >(
     object: T,
diff --git a/src/types.test.ts b/src/types.test.ts
index 5ee4d972..eafd2683 100644
--- a/src/types.test.ts
+++ b/src/types.test.ts
@@ -375,7 +375,7 @@ describe('Support c.json(undefined)', () => {
       '/this/is/a/test': {
         $get: {
           input: {}
-          output: undefined
+          output: never
           outputFormat: 'json'
           status: StatusCode
         }
diff --git a/src/utils/types.test.ts b/src/utils/types.test.ts
index 4f465149..709ea689 100644
--- a/src/utils/types.test.ts
+++ b/src/utils/types.test.ts
@@ -21,6 +21,147 @@ describe('JSONParsed', () => {
     someMeta: Meta
   }
 
+  describe('primitives', () => {
+    it('should convert number type to number', () => {
+      type Actual = JSONParsed<number>
+      type Expected = number
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert string type to string', () => {
+      type Actual = JSONParsed<string>
+      type Expected = string
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert boolean type to boolean', () => {
+      type Actual = JSONParsed<boolean>
+      type Expected = boolean
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert null type to null', () => {
+      type Actual = JSONParsed<null>
+      type Expected = null
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+  })
+
+  describe('toJSON', () => {
+    it('should convert { toJSON() => T } to T', () => {
+      type Actual = JSONParsed<{ toJSON(): number }>
+      type Expected = number
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('toJSON is not called recursively', () => {
+      type Actual = JSONParsed<{ toJSON(): { toJSON(): number } }>
+      type Expected = {}
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert { a: { toJSON() => T } } to { a: T }', () => {
+      type Actual = JSONParsed<{ a: { toJSON(): number } }>
+      type Expected = { a: number }
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+  })
+
+  describe('invalid types', () => {
+    it('should convert undefined type to never', () => {
+      type Actual = JSONParsed<undefined>
+      type Expected = never
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert symbol type to never', () => {
+      type Actual = JSONParsed<symbol>
+      type Expected = never
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert function type to never', () => {
+      type Actual = JSONParsed<() => void>
+      type Expected = never
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+  })
+
+  describe('array', () => {
+    it('should convert undefined[] type to null[]', () => {
+      type Actual = JSONParsed<undefined[]>
+      type Expected = null[]
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert Function[] type to null[]', () => {
+      type Actual = JSONParsed<(() => void)[]>
+      type Expected = null[]
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert symbol[] type to null[]', () => {
+      type Actual = JSONParsed<symbol[]>
+      type Expected = null[]
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert (T | undefined)[] type to JSONParsedT | null>[]', () => {
+      type Actual = JSONParsed<(number | undefined)[]>
+      type Expected = (number | null)[]
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+  })
+
+  describe('tuple', () => {
+    it('should convert [T, S] type to [T, S]', () => {
+      type Actual = JSONParsed<[number, string]>
+      type Expected = [number, string]
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert [T, undefined] type to [T, null]', () => {
+      type Actual = JSONParsed<[number, undefined]>
+      type Expected = [number, null]
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+  })
+
+  describe('object', () => {
+    it('should omit keys with undefined value', () => {
+      type Actual = JSONParsed<{ a: number; b: undefined }>
+      type Expected = { a: number }
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should omit keys with symbol value', () => {
+      type Actual = JSONParsed<{ a: number; b: symbol }>
+      type Expected = { a: number }
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should omit keys with function value', () => {
+      type Actual = JSONParsed<{ a: number; b: () => void }>
+      type Expected = { a: number }
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should omit symbol keys', () => {
+      type Actual = JSONParsed<{ a: number; [x: symbol]: number }>
+      type Expected = { a: number }
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert T | undefined to T | undefined', () => {
+      type Actual = JSONParsed<{ a: number; b: number | undefined }>
+      type Expected = { a: number; b: number | undefined }
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should omit keys with invalid union', () => {
+      type Actual = JSONParsed<{ a: number; b: undefined | symbol }>
+      type Expected = { a: number }
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+  })
+
+  describe('Set/Map', () => {
+    it('should convert Set to empty object', () => {
+      type Actual = JSONParsed<Set<number>>
+      type Expected = {}
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+    it('should convert Map to empty object', () => {
+      type Actual = JSONParsed<Map<number, number>>
+      type Expected = {}
+      expectTypeOf<Actual>().toEqualTypeOf<Expected>()
+    })
+  })
+
   it('Should parse a complex type', () => {
     const sample: JSONParsed<SampleType> = {
       someMeta: {
diff --git a/src/utils/types.ts b/src/utils/types.ts
index 8754a54a..8beb970a 100644
--- a/src/utils/types.ts
+++ b/src/utils/types.ts
@@ -24,21 +24,46 @@ export type RemoveBlankRecord<T> = T extends Record<infer K, unknown>
 
 export type IfAnyThenEmptyObject<T> = 0 extends 1 & T ? {} : T
 
-export type JSONPrimitive = string | boolean | number | null | undefined
+export type JSONPrimitive = string | boolean | number | null
 export type JSONArray = (JSONPrimitive | JSONObject | JSONArray)[]
 export type JSONObject = { [key: string]: JSONPrimitive | JSONArray | JSONObject | object }
+export type InvalidJSONValue = undefined | symbol | ((...args: unknown[]) => unknown)
+
+type InvalidToNull<T> = T extends InvalidJSONValue ? null : T
+
+type IsInvalid<T> = T extends InvalidJSONValue ? true : false
+
+/**
+ * symbol keys are omitted through `JSON.stringify`
+ */
+type OmitSymbolKeys<T> = { [K in keyof T as K extends symbol ? never : K]: T[K] }
+
 export type JSONValue = JSONObject | JSONArray | JSONPrimitive
 // Non-JSON values such as `Date` implement `.toJSON()`, so they can be transformed to a value assignable to `JSONObject`:
 export type JSONParsed<T> = T extends { toJSON(): infer J }
-  ? (() => J) extends () => JSONObject
+  ? (() => J) extends () => JSONPrimitive
     ? J
+    : (() => J) extends () => { toJSON(): unknown }
+    ? {}
     : JSONParsed<J>
   : T extends JSONPrimitive
   ? T
+  : T extends InvalidJSONValue
+  ? never
+  : T extends []
+  ? []
+  : T extends readonly [infer R, ...infer U]
+  ? [JSONParsed<InvalidToNull<R>>, ...JSONParsed<U>]
   : T extends Array<infer U>
-  ? Array<JSONParsed<U>>
+  ? Array<JSONParsed<InvalidToNull<U>>>
+  : T extends Set<unknown> | Map<unknown, unknown>
+  ? {}
   : T extends object
-  ? { [K in keyof T]: JSONParsed<T[K]> }
+  ? {
+      [K in keyof OmitSymbolKeys<T> as IsInvalid<T[K]> extends true
+        ? never
+        : K]: boolean extends IsInvalid<T[K]> ? JSONParsed<T[K]> | undefined : JSONParsed<T[K]>
+    }
   : never
 
 /**