diff --git a/packages/astro/src/core/routing/manifest/create.ts b/packages/astro/src/core/routing/manifest/create.ts
index 379f458eb50f..66f4a74fac39 100644
--- a/packages/astro/src/core/routing/manifest/create.ts
+++ b/packages/astro/src/core/routing/manifest/create.ts
@@ -459,7 +459,7 @@ export function createRouteManifest(
 			else {
 				destination = to.destination
 			}
-			if (destination.startsWith("http")) {
+			if (/^https?:\/\//.test(destination)) {
 				logger.warn('redirects', `Redirecting to an external URL is not officially supported: ${from} -> ${to}`);
 			}
 		}