diff --git a/backend/tests/unit/imageRotation.test.ts b/backend/tests/unit/imageRotation.test.ts
index a42c0ce..5c35a33 100644
--- a/backend/tests/unit/imageRotation.test.ts
+++ b/backend/tests/unit/imageRotation.test.ts
@@ -4,6 +4,13 @@ import path from 'path';
 import sharp from 'sharp';
 import { rotateInPlace } from '../../src/imageProcessing';
 
+// libvips keeps an input file mapped in its operation cache after a pipeline
+// finishes, and Windows will not delete a file that still has an open handle —
+// so the animated-WebP case, which is the one that ends in a rejection, left
+// afterEach unable to remove its own temporary directory. Disabling the cache
+// costs these six tests nothing: every one of them reads its file exactly once.
+sharp.cache(false);
+
 let dir = '';
 
 beforeEach(async () => {