diff --git a/microdroid_manager/src/instance.rs b/microdroid_manager/src/instance.rs
index f3bbf16..4d65421 100644
--- a/microdroid_manager/src/instance.rs
+++ b/microdroid_manager/src/instance.rs
@@ -33,6 +33,8 @@
 //! The payload of a partition is encrypted/signed by a key that is unique to the loader and to the
 //! VM as well. Failing to decrypt/authenticate a partition by a loader stops the boot process.
 
+use crate::ioutil;
+
 use android_security_dice::aidl::android::security::dice::IDiceNode::IDiceNode;
 use anyhow::{anyhow, bail, Context, Result};
 use binder::wait_for_interface;
@@ -180,7 +182,7 @@
 
         // Persist the encrypted payload data
         self.file.write_all(&data)?;
-        self.file.flush()?;
+        ioutil::blkflsbuf(&mut self.file)?;
 
         Ok(())
     }
diff --git a/microdroid_manager/src/ioutil.rs b/microdroid_manager/src/ioutil.rs
index 8ab2413..8ac3712 100644
--- a/microdroid_manager/src/ioutil.rs
+++ b/microdroid_manager/src/ioutil.rs
@@ -14,11 +14,13 @@
 
 //! IO utilities
 
-use anyhow::{anyhow, Result};
+use anyhow::{anyhow, bail, Result};
 use log::debug;
 use std::fmt::Debug;
 use std::fs::File;
 use std::io;
+use std::os::unix::fs::FileTypeExt;
+use std::os::unix::io::AsRawFd;
 use std::path::Path;
 use std::thread;
 use std::time::{Duration, Instant};
@@ -45,6 +47,20 @@
     }
 }
 
+// From include/uapi/linux/fs.h
+const BLK: u8 = 0x12;
+const BLKFLSBUF: u8 = 97;
+nix::ioctl_none!(_blkflsbuf, BLK, BLKFLSBUF);
+
+pub fn blkflsbuf(f: &mut File) -> Result<()> {
+    if !f.metadata()?.file_type().is_block_device() {
+        bail!("{:?} is not a block device", f.as_raw_fd());
+    }
+    // SAFETY: The file is kept open until the end of this function.
+    unsafe { _blkflsbuf(f.as_raw_fd()) }?;
+    Ok(())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
diff --git a/tests/testapk/src/java/com/android/microdroid/test/MicrodroidTests.java b/tests/testapk/src/java/com/android/microdroid/test/MicrodroidTests.java
index 803bdc6..8cfb3a1 100644
--- a/tests/testapk/src/java/com/android/microdroid/test/MicrodroidTests.java
+++ b/tests/testapk/src/java/com/android/microdroid/test/MicrodroidTests.java
@@ -226,11 +226,6 @@
                 new VmEventListener() {
                     @Override
                     public void onPayloadReady(VirtualMachine vm) {
-                        // TODO(b/208639280): remove this sleep. For now, we need to wait for a few
-                        // seconds so that crosvm can actually persist instance.img.
-                        try {
-                            Thread.sleep(30 * 1000);
-                        } catch (InterruptedException e) { }
                         forceStop(vm);
                     }
                 };
@@ -291,11 +286,6 @@
                         } catch (Exception e) {
                             fail("Exception while connecting to service: " + e.toString());
                         }
-                        // TODO(b/208639280): remove this sleep. For now, we need to wait for a few
-                        // seconds so that crosvm can actually persist instance.img.
-                        try {
-                            Thread.sleep(30 * 1000);
-                        } catch (InterruptedException e) { }
                         forceStop(vm);
                     }
                 };