diff --git a/crates/clawhdf5-format/src/global_heap.rs b/crates/clawhdf5-format/src/global_heap.rs
index c6de363..e635d4f 100644
--- a/crates/clawhdf5-format/src/global_heap.rs
+++ b/crates/clawhdf5-format/src/global_heap.rs
@@ -296,8 +296,10 @@ mod tests {
             buf.extend_from_slice(&ref_count.to_le_bytes());
             buf.extend_from_slice(&[0u8; 4]); // reserved
             match length_size {
-                4 => buf.extend_from_slice(&(data.len() as u32).to_le_bytes()),
-                8 => buf.extend_from_slice(&(data.len() as u64).to_le_bytes()),
+                // `<[u8]>::len`: with `Storage` in scope `data.len()` on a
+                // `&&[u8]` resolves to `Storage::len` (a `u64`).
+                4 => buf.extend_from_slice(&(<[u8]>::len(data) as u32).to_le_bytes()),
+                8 => buf.extend_from_slice(&(<[u8]>::len(data) as u64).to_le_bytes()),
                 _ => panic!("unsupported"),
             }
             buf.resize(buf.len() + (pad8(8 + ls) - (8 + ls)), 0);