diff --git a/dist/post/index.js b/dist/post/index.js
index 62881f2..0d62b1f 100644
--- a/dist/post/index.js
+++ b/dist/post/index.js
@@ -36333,7 +36333,9 @@ async function run() {
             core.debug(`${stickyDiskPath} is not mounted, skipping unmount`);
             return;
         }
-        // First try to unmount with retries
+        // Ensure all pending writes are flushed to disk before unmounting.
+        await execAsync('sync');
+        // Unmount with retries.
         for (let attempt = 1; attempt <= 10; attempt++) {
             try {
                 await execAsync(`sudo umount ${stickyDiskPath}`);
diff --git a/src/post.ts b/src/post.ts
index bedff4b..412d19c 100644
--- a/src/post.ts
+++ b/src/post.ts
@@ -80,7 +80,10 @@ async function run(): Promise<void> {
       return;
     }
 
-    // First try to unmount with retries
+    // Ensure all pending writes are flushed to disk before unmounting.
+    await execAsync('sync');
+
+    // Unmount with retries.
     for (let attempt = 1; attempt <= 10; attempt++) {
       try {
         await execAsync(`sudo umount ${stickyDiskPath}`);