diff --git a/src/lib/atproto/index.ts b/src/lib/atproto/index.ts
index 60c2f8f..27b0ad5 100644
--- a/src/lib/atproto/index.ts
+++ b/src/lib/atproto/index.ts
@@ -2,13 +2,15 @@
 import '@atcute/atproto';
 import { createAtprotoAuth } from '@svelte-atproto/oauth/server';
 import { cloudflareKV } from '@svelte-atproto/oauth/server/stores/cloudflare';
+import { building } from '$app/environment';
 import { env } from '$env/dynamic/private';
 import { contrail } from '$lib/contrail';
 
 // To enable signup, add: signupPDS: 'https://your-pds.example/'
 export const atproto = createAtprotoAuth({
 	origin: env.ORIGIN,
-	cookieSecret: env.COOKIE_SECRET,
+	// Cloudflare runtime secrets are unavailable while SvelteKit analyses the build.
+	cookieSecret: env.COOKIE_SECRET || (building ? 'build-only-cookie-secret' : undefined),
 	clientAssertionKey: env.CLIENT_ASSERTION_KEY,
 	scope:
 		'atproto repo:social.popfeed.feed.review repo:social.popfeed.feed.comment repo:social.popfeed.feed.like repo:social.popfeed.feed.list repo:social.popfeed.feed.listItem blob:*/* ' +