diff --git a/.changeset/cold-wasps-flow.md b/.changeset/cold-wasps-flow.md
new file mode 100644
index 000000000000..fd896ed95187
--- /dev/null
+++ b/.changeset/cold-wasps-flow.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Allow ActionData to be undefined
diff --git a/packages/kit/src/core/sync/write_types/index.js b/packages/kit/src/core/sync/write_types/index.js
index a7c82f905059..fc18f0c0eca2 100644
--- a/packages/kit/src/core/sync/write_types/index.js
+++ b/packages/kit/src/core/sync/write_types/index.js
@@ -308,7 +308,7 @@ function process_node(node, outdir, is_page, all_pages_have_load = true) {
 						? `./proxy${replace_ext_with_js(basename)}`
 						: path_to_original(outdir, node.server);
 
-					type = `Expand<Kit.AwaitedActions<typeof import('${from}').actions>>`;
+					type = `Expand<Kit.AwaitedActions<typeof import('${from}').actions>> | undefined`;
 				}
 			}
 			exports.push(`export type ActionData = ${type};`);
diff --git a/packages/kit/src/core/sync/write_types/test/simple-page-server-only/_expected/$types.d.ts b/packages/kit/src/core/sync/write_types/test/simple-page-server-only/_expected/$types.d.ts
index 4b2b444d2b30..597cd9a16ce6 100644
--- a/packages/kit/src/core/sync/write_types/test/simple-page-server-only/_expected/$types.d.ts
+++ b/packages/kit/src/core/sync/write_types/test/simple-page-server-only/_expected/$types.d.ts
@@ -21,9 +21,9 @@ export type PageServerLoad<
 	OutputData extends OutputDataShape<PageServerParentData> = OutputDataShape<PageServerParentData>
 > = Kit.ServerLoad<RouteParams, PageServerParentData, OutputData>;
 export type PageServerLoadEvent = Parameters<PageServerLoad>[0];
-export type ActionData = Expand<
-	Kit.AwaitedActions<typeof import('../../../../../../../../+page.server.js').actions>
->;
+export type ActionData =
+	| Expand<Kit.AwaitedActions<typeof import('../../../../../../../../+page.server.js').actions>>
+	| undefined;
 export type PageServerData = Expand<
 	Kit.AwaitedProperties<
 		Awaited<ReturnType<typeof import('../../../../../../../../+page.server.js').load>>