diff --git a/crates/s3s-fs/src/fs.rs b/crates/s3s-fs/src/fs.rs
index b67fc9a5..9a4c7f18 100644
--- a/crates/s3s-fs/src/fs.rs
+++ b/crates/s3s-fs/src/fs.rs
@@ -15,6 +15,7 @@ use tokio::io::{AsyncReadExt, BufWriter};
 
 use md5::{Digest, Md5};
 use path_absolutize::Absolutize;
+use s3s::dto::PartNumber;
 use uuid::Uuid;
 
 #[derive(Debug)]
@@ -35,7 +36,7 @@ fn clean_old_tmp_files(root: &Path) -> std::io::Result<()> {
         let entry = entry?;
         let file_name = entry.file_name();
         let Some(file_name) = file_name.to_str() else { continue };
-        // See `FileSystem::write_file`
+        // See `FileSystem::prepare_file_write`
         if file_name.starts_with(".tmp.") && file_name.ends_with(".internal.part") {
             std::fs::remove_file(entry.path())?;
         }
@@ -55,6 +56,10 @@ impl FileSystem {
         Ok(path.as_ref().absolutize_virtually(&self.root)?.into_owned())
     }
 
+    pub(crate) fn resolve_upload_part_path(&self, upload_id: Uuid, part_number: PartNumber) -> Result<PathBuf> {
+        self.resolve_abs_path(format!(".upload_id-{upload_id}.part-{part_number}"))
+    }
+
     /// resolve object path under the virtual root
     pub(crate) fn get_object_path(&self, bucket: &str, key: &str) -> Result<PathBuf> {
         let dir = Path::new(&bucket);
@@ -171,53 +176,52 @@ impl FileSystem {
 
     /// Write to the filesystem atomically.
     /// This is done by first writing to a temporary location and then moving the file.
-    pub(crate) async fn prepare_file_write(&self, bucket: &str, key: &str) -> Result<FileWriter> {
-        let final_path = Some(self.get_object_path(bucket, key)?);
+    pub(crate) async fn prepare_file_write<'a>(&self, path: &'a Path) -> Result<FileWriter<'a>> {
         let tmp_name = format!(".tmp.{}.internal.part", self.tmp_file_counter.fetch_add(1, Ordering::SeqCst));
         let tmp_path = self.resolve_abs_path(tmp_name)?;
         let file = File::create(&tmp_path).await?;
         let writer = BufWriter::new(file);
         Ok(FileWriter {
             tmp_path,
-            final_path,
+            dest_path: path,
             writer,
             clean_tmp: true,
         })
     }
 }
 
-pub(crate) struct FileWriter {
+pub(crate) struct FileWriter<'a> {
     tmp_path: PathBuf,
-    final_path: Option<PathBuf>,
+    dest_path: &'a Path,
     writer: BufWriter<File>,
     clean_tmp: bool,
 }
 
-impl FileWriter {
+impl<'a> FileWriter<'a> {
     pub(crate) fn tmp_path(&self) -> &Path {
         &self.tmp_path
     }
 
-    pub(crate) fn final_path(&self) -> &Path {
-        self.final_path.as_ref().unwrap()
+    pub(crate) fn dest_path(&self) -> &'a Path {
+        self.dest_path
     }
 
     pub(crate) fn writer(&mut self) -> &mut BufWriter<File> {
         &mut self.writer
     }
 
-    pub(crate) async fn done(mut self) -> Result<PathBuf> {
-        if let Some(final_dir_path) = self.final_path().parent() {
+    pub(crate) async fn done(mut self) -> Result<()> {
+        if let Some(final_dir_path) = self.dest_path().parent() {
             fs::create_dir_all(&final_dir_path).await?;
         }
 
-        fs::rename(&self.tmp_path, &self.final_path()).await?;
+        fs::rename(&self.tmp_path, self.dest_path()).await?;
         self.clean_tmp = false;
-        Ok(self.final_path.take().unwrap())
+        Ok(())
     }
 }
 
-impl Drop for FileWriter {
+impl<'a> Drop for FileWriter<'a> {
     fn drop(&mut self) {
         if self.clean_tmp {
             let _ = std::fs::remove_file(&self.tmp_path);
diff --git a/crates/s3s-fs/src/s3.rs b/crates/s3s-fs/src/s3.rs
index 49ca2d06..e16fff23 100644
--- a/crates/s3s-fs/src/s3.rs
+++ b/crates/s3s-fs/src/s3.rs
@@ -16,7 +16,6 @@ use std::path::{Path, PathBuf};
 
 use tokio::fs;
 use tokio::io::AsyncSeekExt;
-use tokio::io::BufWriter;
 use tokio_util::io::ReaderStream;
 
 use futures::TryStreamExt;
@@ -466,7 +465,8 @@ impl S3 for FileSystem {
             return Ok(S3Response::new(output));
         }
 
-        let mut file_writer = self.prepare_file_write(&bucket, &key).await?;
+        let object_path = self.get_object_path(&bucket, &key)?;
+        let mut file_writer = self.prepare_file_write(&object_path).await?;
 
         let mut md5_hash = Md5::new();
         let stream = body.inspect_ok(|bytes| {
@@ -475,7 +475,7 @@ impl S3 for FileSystem {
         });
 
         let size = copy_bytes(stream, file_writer.writer()).await?;
-        let object_path = file_writer.done().await?;
+        file_writer.done().await?;
 
         let md5_sum = hex(md5_hash.finalize());
 
@@ -550,15 +550,15 @@ impl S3 for FileSystem {
             return Err(s3_error!(AccessDenied));
         }
 
-        let file_path = self.resolve_abs_path(format!(".upload_id-{upload_id}.part-{part_number}"))?;
+        let file_path = self.resolve_upload_part_path(upload_id, part_number)?;
 
         let mut md5_hash = Md5::new();
         let stream = body.inspect_ok(|bytes| md5_hash.update(bytes.as_ref()));
 
-        let file = try_!(fs::File::create(&file_path).await);
-        let mut writer = BufWriter::new(file);
+        let mut file_writer = self.prepare_file_write(&file_path).await?;
+        let size = copy_bytes(stream, file_writer.writer()).await?;
+        file_writer.done().await?;
 
-        let size = copy_bytes(stream, &mut writer).await?;
         let md5_sum = hex(md5_hash.finalize());
 
         debug!(path = %file_path.display(), ?size, %md5_sum, "write file");
@@ -585,7 +585,7 @@ impl S3 for FileSystem {
             CopySource::Bucket { ref bucket, ref key, .. } => (bucket, key),
         };
         let src_path = self.get_object_path(src_bucket, src_key)?;
-        let dst_path = self.resolve_abs_path(format!(".upload_id-{upload_id}.part-{part_number}"))?;
+        let dst_path = self.resolve_upload_part_path(upload_id, part_number)?;
 
         let mut src_file = fs::File::open(&src_path).await.map_err(|e| s3_error!(e, NoSuchKey))?;
         let file_len = try_!(src_file.metadata().await).len();
@@ -616,13 +616,13 @@ impl S3 for FileSystem {
         let _ = try_!(src_file.seek(io::SeekFrom::Start(start)).await);
         let body = StreamingBlob::wrap(bytes_stream(ReaderStream::with_capacity(src_file, 4096), content_length_usize));
 
-        let dst_file = try_!(fs::File::create(&dst_path).await);
-        let mut writer = BufWriter::new(dst_file);
-
         let mut md5_hash = Md5::new();
         let stream = body.inspect_ok(|bytes| md5_hash.update(bytes.as_ref()));
 
-        let size = copy_bytes(stream, &mut writer).await?;
+        let mut file_writer = self.prepare_file_write(&dst_path).await?;
+        let size = copy_bytes(stream, file_writer.writer()).await?;
+        file_writer.done().await?;
+
         let md5_sum = hex(md5_hash.finalize());
 
         debug!(path = %dst_path.display(), ?size, %md5_sum, "write file");
@@ -707,7 +707,8 @@ impl S3 for FileSystem {
 
         self.delete_upload_id(&upload_id).await?;
 
-        let mut file_writer = self.prepare_file_write(&bucket, &key).await?;
+        let object_path = self.get_object_path(&bucket, &key)?;
+        let mut file_writer = self.prepare_file_write(&object_path).await?;
 
         let mut cnt: i32 = 0;
         for part in multipart_upload.parts.into_iter().flatten() {
@@ -717,15 +718,15 @@ impl S3 for FileSystem {
                 return Err(s3_error!(InvalidRequest, "invalid part order"));
             }
 
-            let part_path = self.resolve_abs_path(format!(".upload_id-{upload_id}.part-{part_number}"))?;
+            let part_path = self.resolve_upload_part_path(upload_id, part_number)?;
 
             let mut reader = try_!(fs::File::open(&part_path).await);
             let size = try_!(tokio::io::copy(&mut reader, &mut file_writer.writer()).await);
 
-            debug!(from = %part_path.display(), tmp = %file_writer.tmp_path().display(), to = %file_writer.final_path().display(), ?size, "write file");
+            debug!(from = %part_path.display(), tmp = %file_writer.tmp_path().display(), to = %file_writer.dest_path().display(), ?size, "write file");
             try_!(fs::remove_file(&part_path).await);
         }
-        let object_path = file_writer.done().await?;
+        file_writer.done().await?;
 
         let file_size = try_!(fs::metadata(&object_path).await).len();
         let md5_sum = self.get_md5_sum(&bucket, &key).await?;