diff --git a/tvix/store/src/blobwriter.rs b/tvix/store/src/blobwriter.rs
index 50471a97c..3966df82d 100644
--- a/tvix/store/src/blobwriter.rs
+++ b/tvix/store/src/blobwriter.rs
@@ -1,7 +1,7 @@
-use crate::chunkservice::ChunkService;
+use crate::chunkservice::{upload_chunk, ChunkService};
 use crate::{proto, Error};
 use rayon::prelude::*;
-use tracing::{debug, instrument};
+use tracing::instrument;
 
 pub struct BlobWriter<'a, CS: ChunkService> {
     chunk_service: &'a CS,
@@ -14,31 +14,6 @@ pub struct BlobWriter<'a, CS: ChunkService> {
     buf: Vec<u8>,
 }
 
-// upload a chunk to the chunk service, and return its digest (or an error) when done.
-#[instrument(skip_all)]
-fn upload_chunk<CS: ChunkService>(
-    chunk_service: &CS,
-    chunk_data: Vec<u8>,
-) -> Result<Vec<u8>, Error> {
-    let mut hasher = blake3::Hasher::new();
-    // TODO: benchmark this number and factor it out
-    if chunk_data.len() >= 128 * 1024 {
-        hasher.update_rayon(&chunk_data);
-    } else {
-        hasher.update(&chunk_data);
-    }
-    let digest = hasher.finalize();
-
-    if chunk_service.has(digest.as_bytes())? {
-        debug!("already has chunk, skipping");
-    }
-    let digest_resp = chunk_service.put(chunk_data)?;
-
-    assert_eq!(digest_resp, digest.as_bytes());
-
-    Ok(digest.as_bytes().to_vec())
-}
-
 impl<'a, CS: ChunkService> BlobWriter<'a, CS> {
     pub fn new(chunk_service: &'a CS) -> Self {
         Self {
diff --git a/tvix/store/src/chunkservice/mod.rs b/tvix/store/src/chunkservice/mod.rs
index 83c91fd96..725ed2014 100644
--- a/tvix/store/src/chunkservice/mod.rs
+++ b/tvix/store/src/chunkservice/mod.rs
@@ -1,3 +1,5 @@
+mod util;
+
 pub mod memory;
 pub mod sled;
 
@@ -5,6 +7,7 @@ use crate::Error;
 
 pub use self::memory::MemoryChunkService;
 pub use self::sled::SledChunkService;
+pub use self::util::upload_chunk;
 
 /// The base trait all ChunkService services need to implement.
 /// It allows checking for the existence, download and upload of chunks.
diff --git a/tvix/store/src/chunkservice/util.rs b/tvix/store/src/chunkservice/util.rs
new file mode 100644
index 000000000..cf644fa51
--- /dev/null
+++ b/tvix/store/src/chunkservice/util.rs
@@ -0,0 +1,30 @@
+use tracing::{debug, instrument};
+
+use crate::Error;
+
+use super::ChunkService;
+
+// upload a chunk to the chunk service, and return its digest (or an error) when done.
+#[instrument(skip_all, err)]
+pub fn upload_chunk<CS: ChunkService>(
+    chunk_service: &CS,
+    chunk_data: Vec<u8>,
+) -> Result<Vec<u8>, Error> {
+    let mut hasher = blake3::Hasher::new();
+    // TODO: benchmark this number and factor it out
+    if chunk_data.len() >= 128 * 1024 {
+        hasher.update_rayon(&chunk_data);
+    } else {
+        hasher.update(&chunk_data);
+    }
+    let digest = hasher.finalize();
+
+    if chunk_service.has(digest.as_bytes())? {
+        debug!("already has chunk, skipping");
+    }
+    let digest_resp = chunk_service.put(chunk_data)?;
+
+    assert_eq!(digest_resp, digest.as_bytes());
+
+    Ok(digest.as_bytes().to_vec())
+}