diff --git a/src/reader/ai-images.js b/src/reader/ai-images.js
index 0eaa46f..c406927 100644
--- a/src/reader/ai-images.js
+++ b/src/reader/ai-images.js
@@ -125,7 +125,9 @@ function cleanup(referencedIds, options) {
   let removed = 0;
   for (const blob of listBlobs()) {
     if (keep.has(blob.imageId)) continue;
-    if (now - blob.mtimeMs < graceMs) continue;
+    // mtimeMs 在 ext4/APFS 上带亚毫秒小数，而 Date.now() 只到整毫秒，
+    // 刚落盘的文件算出来的年龄会是负数，graceMs 为 0 时也永远删不掉
+    if (now - Math.floor(blob.mtimeMs) < graceMs) continue;
     try {
       fs.unlinkSync(blob.file);
       removed++;