diff --git a/.changeset/fluffy-ants-reflect.md b/.changeset/fluffy-ants-reflect.md
new file mode 100644
index 0000000000..924c799104
--- /dev/null
+++ b/.changeset/fluffy-ants-reflect.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a regression that caused `default()` to not work with `reference()`
diff --git a/packages/astro/src/content/runtime.ts b/packages/astro/src/content/runtime.ts
index cf6537609e..ea1527106c 100644
--- a/packages/astro/src/content/runtime.ts
+++ b/packages/astro/src/content/runtime.ts
@@ -18,7 +18,7 @@ import {
 	unescapeHTML,
 } from '../runtime/server/index.js';
 import { CONTENT_LAYER_TYPE, IMAGE_IMPORT_PREFIX } from './consts.js';
-import { type DataEntry, globalDataStore } from './data-store.js';
+import { type DataEntry, type ImmutableDataStore, globalDataStore } from './data-store.js';
 import type { ContentLookupMap } from './utils.js';
 
 type LazyImport = () => Promise<any>;
@@ -604,6 +604,10 @@ async function render({
 }
 
 export function createReference({ lookupMap }: { lookupMap: ContentLookupMap }) {
+	// We're handling it like this to avoid needing an async schema. Not ideal, but should
+	// be safe because the store will already have been loaded by the time this is called.
+	let store: ImmutableDataStore | null = null;
+	globalDataStore.get().then((s) => (store = s));
 	return function reference(collection: string) {
 		return z
 			.union([
@@ -618,15 +622,22 @@ export function createReference({ lookupMap }: { lookupMap: ContentLookupMap })
 				}),
 			])
 			.transform(
-				async (
+				(
 					lookup:
 						| string
 						| { id: string; collection: string }
 						| { slug: string; collection: string },
 					ctx,
 				) => {
+					if (!store) {
+						ctx.addIssue({
+							code: ZodIssueCode.custom,
+							message: `**${ctx.path.join('.')}:** Reference to ${collection} could not be resolved: store not available.\nThis is an Astro bug, so please file an issue at https://github.com/withastro/astro/issues.`,
+						});
+						return;
+					}
+
 					const flattenedErrorPath = ctx.path.join('.');
-					const store = await globalDataStore.get();
 					const collectionIsInStore = store.hasCollection(collection);
 
 					if (typeof lookup === 'object') {
diff --git a/packages/astro/test/fixtures/content-layer/src/content.config.ts b/packages/astro/test/fixtures/content-layer/src/content.config.ts
index b0e9722565..484d14d528 100644
--- a/packages/astro/test/fixtures/content-layer/src/content.config.ts
+++ b/packages/astro/test/fixtures/content-layer/src/content.config.ts
@@ -152,7 +152,7 @@ const spacecraft = defineCollection({
 			publishedDate: z.coerce.date(),
 			tags: z.array(z.string()),
 			heroImage: image().optional(),
-			cat: reference('cats').optional(),
+			cat: reference('cats').default('siamese'),
 			something: z
 				.string()
 				.optional()