diff --git a/virtualizationservice/src/aidl.rs b/virtualizationservice/src/aidl.rs
index 44d89e7..12c46ee 100644
--- a/virtualizationservice/src/aidl.rs
+++ b/virtualizationservice/src/aidl.rs
@@ -35,13 +35,13 @@
 use android_system_virtualizationservice::binder::{
     self, BinderFeatures, ExceptionCode, Interface, ParcelFileDescriptor, Status, Strong, ThreadState,
 };
-use anyhow::{bail, Result};
+use anyhow::{bail, Context, Result};
 use disk::QcowFile;
 use log::{debug, error, warn, info};
 use microdroid_payload_config::{ApexConfig, VmPayloadConfig};
 use std::convert::TryInto;
 use std::ffi::CString;
-use std::fs::{File, create_dir};
+use std::fs::{File, OpenOptions, create_dir};
 use std::num::NonZeroU32;
 use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd};
 use std::path::{Path, PathBuf};
@@ -67,6 +67,10 @@
 /// payload output
 const PORT_VIRT_SERVICE: u32 = 3000;
 
+/// The size of zero.img.
+/// Gaps in composite disk images are filled with a shared zero.img.
+const ZERO_FILLER_SIZE: u64 = 4096;
+
 /// Implementation of `IVirtualizationService`, the entry point of the AIDL service.
 #[derive(Debug, Default)]
 pub struct VirtualizationService {
@@ -128,6 +132,16 @@
         };
         let config = config.as_ref();
 
+        let zero_filler_path = temporary_directory.join("zero.img");
+        let zero_filler_file = write_zero_filler(&zero_filler_path).map_err(|e| {
+            error!("Failed to make composite image: {}", e);
+            new_binder_exception(
+                ExceptionCode::SERVICE_SPECIFIC,
+                format!("Failed to make composite image: {}", e),
+            )
+        })?;
+        indirect_files.push(zero_filler_file);
+
         // Assemble disk images if needed.
         let disks = config
             .disks
@@ -135,6 +149,7 @@
             .map(|disk| {
                 assemble_disk_image(
                     disk,
+                    &zero_filler_path,
                     &temporary_directory,
                     &mut next_temporary_image_id,
                     &mut indirect_files,
@@ -281,11 +296,23 @@
     Ok(())
 }
 
+fn write_zero_filler(zero_filler_path: &Path) -> Result<File> {
+    let file = OpenOptions::new()
+        .create_new(true)
+        .read(true)
+        .write(true)
+        .open(zero_filler_path)
+        .with_context(|| "Failed to create zero.img")?;
+    file.set_len(ZERO_FILLER_SIZE)?;
+    Ok(file)
+}
+
 /// Given the configuration for a disk image, assembles the `DiskFile` to pass to crosvm.
 ///
 /// This may involve assembling a composite disk from a set of partition images.
 fn assemble_disk_image(
     disk: &DiskImage,
+    zero_filler_path: &Path,
     temporary_directory: &Path,
     next_temporary_image_id: &mut u64,
     indirect_files: &mut Vec<File>,
@@ -303,6 +330,7 @@
             make_composite_image_filenames(temporary_directory, next_temporary_image_id);
         let (image, partition_files) = make_composite_image(
             &disk.partitions,
+            zero_filler_path,
             &composite_image_filenames.composite,
             &composite_image_filenames.header,
             &composite_image_filenames.footer,
diff --git a/virtualizationservice/src/composite.rs b/virtualizationservice/src/composite.rs
index ed277e6..378ed78 100644
--- a/virtualizationservice/src/composite.rs
+++ b/virtualizationservice/src/composite.rs
@@ -73,7 +73,7 @@
 }
 
 /// Round `val` to partition size(4K)
-pub fn align_to_partition_size(val: u64) -> u64 {
+fn align_to_partition_size(val: u64) -> u64 {
     align_to_power_of_2(val, PARTITION_SIZE_SHIFT)
 }
 
@@ -168,7 +168,7 @@
 fn create_component_disks(
     partition: &PartitionInfo,
     offset: u64,
-    header_path: &str,
+    zero_filler_path: &str,
 ) -> Result<Vec<ComponentDisk>, Error> {
     let aligned_size = partition.aligned_size();
 
@@ -208,7 +208,7 @@
             );
             component_disks.push(ComponentDisk {
                 offset: offset + file_size_sum,
-                file_path: header_path.to_owned(),
+                file_path: zero_filler_path.to_owned(),
                 read_write_capability: ReadWriteCapability::READ_ONLY,
                 ..ComponentDisk::new()
             });
@@ -222,19 +222,22 @@
 /// files.
 pub fn create_composite_disk(
     partitions: &[PartitionInfo],
+    zero_filler_path: &Path,
     header_path: &Path,
     header_file: &mut File,
     footer_path: &Path,
     footer_file: &mut File,
     output_composite: &mut File,
 ) -> Result<(), Error> {
+    let zero_filler_path =
+        zero_filler_path.to_str().context("Invalid zero filler path")?.to_string();
     let header_path = header_path.to_str().context("Invalid header path")?.to_string();
     let footer_path = footer_path.to_str().context("Invalid footer path")?.to_string();
 
     let mut composite_proto = CompositeDisk::new();
     composite_proto.version = COMPOSITE_DISK_VERSION;
     composite_proto.component_disks.push(ComponentDisk {
-        file_path: header_path.clone(),
+        file_path: header_path,
         offset: 0,
         read_write_capability: ReadWriteCapability::READ_ONLY,
         ..ComponentDisk::new()
@@ -249,7 +252,9 @@
     for partition in partitions {
         create_gpt_entry(partition, next_disk_offset).write_bytes(&mut writer)?;
 
-        for component_disk in create_component_disks(partition, next_disk_offset, &header_path)? {
+        for component_disk in
+            create_component_disks(partition, next_disk_offset, &zero_filler_path)?
+        {
             composite_proto.component_disks.push(component_disk);
         }
 
@@ -304,6 +309,7 @@
 /// the form `/proc/self/fd/N` for the partition images.
 pub fn make_composite_image(
     partitions: &[Partition],
+    zero_filler_path: &Path,
     output_path: &Path,
     header_path: &Path,
     footer_path: &Path,
@@ -327,6 +333,7 @@
 
     create_composite_disk(
         &partitions,
+        zero_filler_path,
         header_path,
         &mut header_file,
         footer_path,
diff --git a/virtualizationservice/src/payload.rs b/virtualizationservice/src/payload.rs
index 1df537c..9c6deae 100644
--- a/virtualizationservice/src/payload.rs
+++ b/virtualizationservice/src/payload.rs
@@ -14,17 +14,13 @@
 
 //! Payload disk image
 
-use crate::composite::align_to_partition_size;
-
 use anyhow::{anyhow, Context, Result};
 use microdroid_metadata::{ApexPayload, ApkPayload, Metadata};
 use microdroid_payload_config::ApexConfig;
 use once_cell::sync::OnceCell;
 use serde::Deserialize;
 use serde_xml_rs::from_reader;
-use std::fs;
 use std::fs::{File, OpenOptions};
-use std::io::{Seek, SeekFrom, Write};
 use std::path::{Path, PathBuf};
 use vmconfig::{DiskImage, Partition};
 
@@ -69,46 +65,12 @@
     }
 }
 
-/// When passing a host APEX file as a block device in a payload disk image,
-/// the size of the original file needs to be stored in the last 4 bytes so that
-/// other programs (e.g. apexd) can read it as a zip.
-/// Returns true always since the filler is created.
-fn make_size_filler(size: u64, filler_path: &Path) -> Result<bool> {
-    let partition_size = align_to_partition_size(size + 4);
-    let mut file = OpenOptions::new().create_new(true).write(true).open(filler_path)?;
-    file.set_len(partition_size - size)?;
-    file.seek(SeekFrom::End(-4))?;
-    file.write_all(&(size as i32).to_be_bytes())?;
-    Ok(true)
-}
-
-/// When passing a host APK file as a block device in a payload disk image and it is
-/// mounted via dm-verity, we need to make the device zero-padded up to 4K boundary.
-/// Otherwise, integrity checks via hashtree will fail.
-/// Returns true if filler is created.
-fn make_zero_filler(size: u64, filler_path: &Path) -> Result<bool> {
-    let partition_size = align_to_partition_size(size);
-    if partition_size <= size {
-        return Ok(false);
-    }
-    let file = OpenOptions::new().create_new(true).write(true).open(filler_path)?;
-    file.set_len(partition_size - size)?;
-    Ok(true)
-}
-
-/// When passing a host idsig file as a block device, we don't need any filler because it is read
-/// in length-prefixed way.
-/// Returns false always because the filler is not created.
-fn make_no_filler(_size: u64, _filler_path: &Path) -> Result<bool> {
-    Ok(false)
-}
-
 /// Creates a DiskImage with partitions:
 ///   metadata: metadata
-///   microdroid-apex-0: [apex 0, size filler]
-///   microdroid-apex-1: [apex 1, size filler]
+///   microdroid-apex-0: apex 0
+///   microdroid-apex-1: apex 1
 ///   ..
-///   microdroid-apk: [apk, zero filler]
+///   microdroid-apk: apk
 ///   microdroid-apk-idsig: idsig
 pub fn make_payload_disk(
     apk_file: PathBuf,
@@ -146,48 +108,23 @@
     }];
 
     let apex_info_list = ApexInfoList::load()?;
-    let mut filler_count = 0;
     for (i, apex) in apexes.iter().enumerate() {
-        partitions.push(make_partition(
-            format!("microdroid-apex-{}", i),
-            apex_info_list.get_path_for(&apex.name)?,
-            temporary_directory,
-            &mut filler_count,
-            &make_size_filler,
-        )?);
+        partitions.push(Partition {
+            label: format!("microdroid-apex-{}", i),
+            paths: vec![apex_info_list.get_path_for(&apex.name)?],
+            writable: false,
+        });
     }
-    partitions.push(make_partition(
-        "microdroid-apk".to_owned(),
-        apk_file,
-        temporary_directory,
-        &mut filler_count,
-        &make_zero_filler,
-    )?);
-    partitions.push(make_partition(
-        "microdroid-apk-idsig".to_owned(),
-        idsig_file,
-        temporary_directory,
-        &mut filler_count,
-        &make_no_filler,
-    )?);
+    partitions.push(Partition {
+        label: "microdroid-apk".to_owned(),
+        paths: vec![apk_file],
+        writable: false,
+    });
+    partitions.push(Partition {
+        label: "microdroid-apk-idsig".to_owned(),
+        paths: vec![idsig_file],
+        writable: false,
+    });
 
     Ok(DiskImage { image: None, partitions, writable: false })
 }
-
-fn make_partition(
-    label: String,
-    path: PathBuf,
-    temporary_directory: &Path,
-    filler_count: &mut u32,
-    make_filler: &dyn Fn(u64, &Path) -> Result<bool>,
-) -> Result<Partition> {
-    let filler_path = temporary_directory.join(format!("filler-{}", filler_count));
-    let size = fs::metadata(&path)?.len();
-
-    if make_filler(size, &filler_path)? {
-        *filler_count += 1;
-        Ok(Partition { label, paths: vec![path, filler_path], writable: false })
-    } else {
-        Ok(Partition { label, paths: vec![path], writable: false })
-    }
-}