diff --git a/crates/clawhdf5-format/src/fill_value.rs b/crates/clawhdf5-format/src/fill_value.rs
index 88cbc3f..6ab3460 100644
--- a/crates/clawhdf5-format/src/fill_value.rs
+++ b/crates/clawhdf5-format/src/fill_value.rs
@@ -111,17 +111,24 @@ pub fn dataset_fill_value(messages: &[HeaderMessage]) -> Result<Option<Vec<u8>>,
 /// fill value message to where it lives: another object header, or the
 /// file's shared-message (SOHM) heap, as libhdf5 writes it when the file has
 /// a SOHM index for fill values.
-///
-/// `file_data` is any [`Storage`](crate::storage::Storage): the file as a
-/// `&[u8]`, or a backend that serves it by range. (The trait is not
-/// imported here: its `len` would shadow the slice method in this module.)
-pub fn dataset_fill_value_in<S: crate::storage::Storage + ?Sized>(
-    file_data: &S,
+pub fn dataset_fill_value_in(
+    file_data: &[u8],
+    messages: &[HeaderMessage],
+    offset_size: u8,
+    length_size: u8,
+) -> Result<Option<Vec<u8>>, FormatError> {
+    dataset_fill_value_from_storage(&file_data, messages, offset_size, length_size)
+}
+
+/// [`dataset_fill_value_in`] with the file behind any
+/// [`Storage`](crate::storage::Storage). (The trait is not imported here:
+/// its `len` would shadow the slice method in this module.)
+pub fn dataset_fill_value_from_storage(
+    file: &dyn crate::storage::Storage,
     messages: &[HeaderMessage],
     offset_size: u8,
     length_size: u8,
 ) -> Result<Option<Vec<u8>>, FormatError> {
-    let file: &dyn crate::storage::Storage = &file_data;
     fill_value_from(messages, |msg| {
         crate::shared_message::message_data_with_sohm_in(file, msg, offset_size, length_size)
             .map(|data| data.into_owned())
@@ -472,7 +479,7 @@ mod tests {
                 .count();
             let want = dataset_fill_value_in(file, &h.messages, os, ls);
             assert_eq!(want, Ok(Some((-7i32).to_le_bytes().to_vec())));
-            let got = dataset_fill_value_in(&storage, &h.messages, os, ls);
+            let got = dataset_fill_value_from_storage(&storage, &h.messages, os, ls);
             assert_eq!(got, want, "{}", child.name);
         }
         assert!(shared >= 2);
diff --git a/crates/clawhdf5-format/tests/storage_equivalence.rs b/crates/clawhdf5-format/tests/storage_equivalence.rs
index a046ffb..ada6274 100644
--- a/crates/clawhdf5-format/tests/storage_equivalence.rs
+++ b/crates/clawhdf5-format/tests/storage_equivalence.rs
@@ -44,7 +44,7 @@ use clawhdf5_format::error::FormatError;
 use clawhdf5_format::extensible_array::{
     ExtensibleArrayHeader, read_extensible_array_chunks, read_extensible_array_chunks_in,
 };
-use clawhdf5_format::fill_value::dataset_fill_value_in;
+use clawhdf5_format::fill_value::{dataset_fill_value_from_storage, dataset_fill_value_in};
 use clawhdf5_format::fixed_array::{
     FixedArrayHeader, read_fixed_array_chunks, read_fixed_array_chunks_in,
 };
@@ -189,7 +189,7 @@ impl Walk<'_> {
         self.same(
             "fill value",
             &want,
-            &dataset_fill_value_in(self.storage, &header.messages, os, ls),
+            &dataset_fill_value_from_storage(self.st(), &header.messages, os, ls),
         );
 
         for msg in &header.messages {