diff --git a/crates/clawhdf5-format/src/fill_value.rs b/crates/clawhdf5-format/src/fill_value.rs
index 3b18790..88cbc3f 100644
--- a/crates/clawhdf5-format/src/fill_value.rs
+++ b/crates/clawhdf5-format/src/fill_value.rs
@@ -111,14 +111,19 @@ 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.
-pub fn dataset_fill_value_in(
-    file_data: &[u8],
+///
+/// `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,
     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(file_data, msg, offset_size, length_size)
+        crate::shared_message::message_data_with_sohm_in(file, msg, offset_size, length_size)
             .map(|data| data.into_owned())
     })
 }
@@ -439,4 +444,37 @@ mod tests {
             .collect();
         assert_eq!(filled, [2, 3, 7, 8]);
     }
+
+    /// Fill values, shared ones in the SOHM heap included, resolve
+    /// identically through a read_at-only CountingStorage.
+    #[test]
+    fn storage_reads_match_slice_reads() {
+        use crate::object_header::ObjectHeader;
+        use crate::storage::CountingStorage;
+        let file: &[u8] = include_bytes!("../tests/fixtures/shared_fill_value.h5");
+        let sb = crate::superblock::Superblock::parse(file, 0).unwrap();
+        let (os, ls) = (sb.offset_size, sb.length_size);
+        let storage = CountingStorage::new(file.to_vec());
+        let mut shared = 0;
+        let children =
+            crate::group_v2::resolve_group_children(file, &sb, sb.root_group_address).unwrap();
+        assert!(children.len() >= 3);
+        for child in children {
+            let h =
+                ObjectHeader::parse(file, child.object_header_address as usize, os, ls).unwrap();
+            shared += h
+                .messages
+                .iter()
+                .filter(|m| {
+                    m.msg_type == MessageType::FillValue
+                        && crate::shared_message::is_shared(m.flags)
+                })
+                .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);
+            assert_eq!(got, want, "{}", child.name);
+        }
+        assert!(shared >= 2);
+    }
 }