diff --git a/virtualizationservice/src/aidl.rs b/virtualizationservice/src/aidl.rs
index 64d3913..dc38075 100644
--- a/virtualizationservice/src/aidl.rs
+++ b/virtualizationservice/src/aidl.rs
@@ -128,14 +128,13 @@
         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| {
+        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
@@ -291,7 +290,7 @@
     Ok(())
 }
 
-fn write_zero_filler(zero_filler_path: &Path) -> Result<File> {
+fn write_zero_filler(zero_filler_path: &Path) -> Result<()> {
     let file = OpenOptions::new()
         .create_new(true)
         .read(true)
@@ -299,7 +298,7 @@
         .open(zero_filler_path)
         .with_context(|| "Failed to create zero.img")?;
     file.set_len(ZERO_FILLER_SIZE)?;
-    Ok(file)
+    Ok(())
 }
 
 /// Given the configuration for a disk image, assembles the `DiskFile` to pass to crosvm.
diff --git a/virtualizationservice/src/composite.rs b/virtualizationservice/src/composite.rs
index 685d0e6..ded0053 100644
--- a/virtualizationservice/src/composite.rs
+++ b/virtualizationservice/src/composite.rs
@@ -290,9 +290,9 @@
 
 /// Constructs a composite disk image for the given list of partitions, and opens it ready to use.
 ///
-/// Returns the composite disk image file, and a list of FD mappings which must be applied to any
-/// process which wants to use it. This is necessary because the composite image contains paths of
-/// the form `/proc/self/fd/N` for the partition images.
+/// Returns the composite disk image file, and a list of files whose file descriptors must be passed
+/// to any process which wants to use it. This is necessary because the composite image contains
+/// paths of the form `/proc/self/fd/N` for the partition images.
 pub fn make_composite_image(
     partitions: &[Partition],
     zero_filler_path: &Path,
@@ -300,7 +300,7 @@
     header_path: &Path,
     footer_path: &Path,
 ) -> Result<(File, Vec<File>), Error> {
-    let (partitions, files) = convert_partitions(partitions)?;
+    let (partitions, mut files) = convert_partitions(partitions)?;
 
     let mut composite_image = OpenOptions::new()
         .create_new(true)
@@ -316,13 +316,16 @@
         OpenOptions::new().create_new(true).read(true).write(true).open(footer_path).with_context(
             || format!("Failed to create composite image header {:?}", footer_path),
         )?;
+    let zero_filler_file = File::open(&zero_filler_path).with_context(|| {
+        format!("Failed to open composite image zero filler {:?}", zero_filler_path)
+    })?;
 
     create_composite_disk(
         &partitions,
-        zero_filler_path,
-        header_path,
+        &fd_path_for_file(&zero_filler_file),
+        &fd_path_for_file(&header_file),
         &mut header_file,
-        footer_path,
+        &fd_path_for_file(&footer_file),
         &mut footer_file,
         &mut composite_image,
     )?;
@@ -331,12 +334,16 @@
     let composite_image = File::open(&output_path)
         .with_context(|| format!("Failed to open composite image {:?}", output_path))?;
 
+    files.push(header_file);
+    files.push(footer_file);
+    files.push(zero_filler_file);
+
     Ok((composite_image, files))
 }
 
 /// Given the AIDL config containing a list of partitions, with a [`ParcelFileDescriptor`] for each
-/// partition, return the list of file descriptors which must be passed to the composite disk image
-/// partition configuration for it.
+/// partition, returns the corresponding list of PartitionInfo and the list of files whose file
+/// descriptors must be passed to any process using the composite image.
 fn convert_partitions(partitions: &[Partition]) -> Result<(Vec<PartitionInfo>, Vec<File>), Error> {
     // File descriptors to pass to child process.
     let mut files = vec![];
@@ -353,12 +360,12 @@
                 .try_clone()
                 .context("Failed to clone partition image file descriptor")?;
             let size = get_partition_size(&file)?;
-            let fd = file.as_raw_fd();
+            let path = fd_path_for_file(&file);
             files.push(file);
 
             Ok(PartitionInfo {
                 label: partition.label.to_owned(),
-                path: format!("/proc/self/fd/{}", fd).into(),
+                path,
                 partition_type: ImagePartitionType::LinuxFilesystem,
                 writable: partition.writable,
                 size,
@@ -369,6 +376,11 @@
     Ok((partitions, files))
 }
 
+fn fd_path_for_file(file: &File) -> PathBuf {
+    let fd = file.as_raw_fd();
+    format!("/proc/self/fd/{}", fd).into()
+}
+
 /// Find the size of the partition image in the given file by parsing the header.
 ///
 /// This will work for raw, QCOW2, composite and Android sparse images.