diff --git a/.changeset/little-onions-relax.md b/.changeset/little-onions-relax.md
new file mode 100644
index 000000000000..820b0a40ebd3
--- /dev/null
+++ b/.changeset/little-onions-relax.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix asset optimization failing when outDir is outside the project directory
diff --git a/packages/astro/src/assets/build/generate.ts b/packages/astro/src/assets/build/generate.ts
index dfc0d9a0d25f..613b80ee04fb 100644
--- a/packages/astro/src/assets/build/generate.ts
+++ b/packages/astro/src/assets/build/generate.ts
@@ -7,6 +7,7 @@ import { getConfiguredImageService, isESMImportedImage } from '../internal.js';
 import type { LocalImageService } from '../services/service.js';
 import type { ImageMetadata, ImageTransform } from '../types.js';
 import { loadRemoteImage, type RemoteCacheEntry } from './remote.js';
+import { getOutDirWithinCwd } from "../../core/build/common.js";
 
 interface GenerationDataUncached {
 	cached: false;
@@ -48,7 +49,7 @@ export async function generateImage(
 		serverRoot = config.build.server;
 		clientRoot = config.build.client;
 	} else {
-		serverRoot = config.outDir;
+		serverRoot = getOutDirWithinCwd(config.outDir);
 		clientRoot = config.outDir;
 	}