diff --git a/.changeset/purple-readers-build.md b/.changeset/purple-readers-build.md
new file mode 100644
index 000000000000..762698421322
--- /dev/null
+++ b/.changeset/purple-readers-build.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+`RequestHandlerOutput` accepts body when it has or maybe is `undefined`
diff --git a/packages/kit/test/typings/endpoint.test.ts b/packages/kit/test/typings/endpoint.test.ts
index f805a811d4a4..9f5af8ec3fc5 100644
--- a/packages/kit/test/typings/endpoint.test.ts
+++ b/packages/kit/test/typings/endpoint.test.ts
@@ -5,10 +5,11 @@ const valid_body = {
 	num: 12345,
 	bool: true,
 	null: null,
+	maybe: Math.random() < 0.5 ? undefined : true,
 	custom: {
 		toJSON: () => 'custom toJSON function'
 	},
-	list: ['string', 12345, false, null],
+	list: ['string', 12345, false, null, undefined],
 	nested: {
 		another: 'string',
 		big_num: 98765,
@@ -84,13 +85,6 @@ export const differential_headers_assignment: RequestHandler = () => {
 
 // --- invalid cases ---
 
-// @ts-expect-error - should not have undefined (should it not?)
-export const error_no_undefined: RequestHandler = () => {
-	return {
-		body: { no: Math.random() < 0.5 ? undefined : 'something' }
-	};
-};
-
 // @ts-expect-error - body must be JSON serializable
 export const error_body_must_be_serializable: RequestHandler = () => {
 	return {
diff --git a/packages/kit/types/private.d.ts b/packages/kit/types/private.d.ts
index d51d7864e645..33b8d487f272 100644
--- a/packages/kit/types/private.d.ts
+++ b/packages/kit/types/private.d.ts
@@ -208,7 +208,15 @@ export type HttpMethod = 'get' | 'head' | 'post' | 'put' | 'delete' | 'patch';
 
 export type JSONObject = { [key: string]: JSONValue };
 
-export type JSONValue = string | number | boolean | null | ToJSON | JSONValue[] | JSONObject;
+export type JSONValue =
+	| string
+	| number
+	| boolean
+	| null
+	| undefined
+	| ToJSON
+	| JSONValue[]
+	| JSONObject;
 
 export interface LoadInput<Params = Record<string, string>> {
 	url: URL;