diff --git a/crates/clawhdf5-format/src/object_header.rs b/crates/clawhdf5-format/src/object_header.rs
index d0f36db..1fa4b41 100644
--- a/crates/clawhdf5-format/src/object_header.rs
+++ b/crates/clawhdf5-format/src/object_header.rs
@@ -385,13 +385,13 @@ impl ObjectHeader {
         }
 
         let chunk0_msg_start = pos;
-        let chunk0_msg_end = abs(pos)
-            .checked_add(chunk0_size)
-            .ok_or(FormatError::UnexpectedEof {
+        let Some(chunk0_abs_end) = abs(pos).checked_add(chunk0_size) else {
+            return Err(FormatError::UnexpectedEof {
                 expected: usize::MAX,
                 available: file_len,
-            })?
-            - base;
+            });
+        };
+        let chunk0_msg_end = chunk0_abs_end - base;
 
         // The whole first chunk, prefix to checksum, in one read (its
         // bounds check is the one on the checksum's 4 bytes).
@@ -1364,7 +1364,11 @@ mod tests {
                     let want = ObjectHeader::parse(&f, at, 8, 8);
                     let storage = CountingStorage::new(f.clone());
                     let got = ObjectHeader::parse_in(&storage, at as u64, 8, 8);
-                    assert_eq!(format!("{got:?}"), format!("{want:?}"), "at {at}, cut {cut}");
+                    assert_eq!(
+                        format!("{got:?}"),
+                        format!("{want:?}"),
+                        "at {at}, cut {cut}"
+                    );
                 }
             }
         }
diff --git a/crates/clawhdf5-format/src/storage.rs b/crates/clawhdf5-format/src/storage.rs
index 76f1436..fb19f32 100644
--- a/crates/clawhdf5-format/src/storage.rs
+++ b/crates/clawhdf5-format/src/storage.rs
@@ -215,7 +215,11 @@ pub fn read_exact_at(
 /// storage. For structures whose size is only known once their prefix has
 /// been parsed and whose parsers bound-check what they are given.
 #[inline]
-pub fn read_upto(file: &dyn Storage, offset: u64, max: usize) -> Result<Cow<'_, [u8]>, FormatError> {
+pub fn read_upto(
+    file: &dyn Storage,
+    offset: u64,
+    max: usize,
+) -> Result<Cow<'_, [u8]>, FormatError> {
     let avail = file.len().saturating_sub(offset);
     let len = usize::try_from(avail).map_or(max, |a| a.min(max));
     let bytes = file.read_at(offset, len)?;
diff --git a/crates/clawhdf5-format/src/superblock_ext.rs b/crates/clawhdf5-format/src/superblock_ext.rs
index 40efd5c..1a684f6 100644
--- a/crates/clawhdf5-format/src/superblock_ext.rs
+++ b/crates/clawhdf5-format/src/superblock_ext.rs
@@ -520,7 +520,10 @@ fn image_block_in(
 }
 
 /// Where the image block is, checked against a file of `file_len` bytes.
-fn image_block_range(file_len: u64, location: CacheImageLocation) -> Result<(u64, usize), FormatError> {
+fn image_block_range(
+    file_len: u64,
+    location: CacheImageLocation,
+) -> Result<(u64, usize), FormatError> {
     let bad = FormatError::InvalidCacheImage;
     let start = usize::try_from(location.address).map_err(|_| bad("address out of range"))?;
     let len = usize::try_from(location.length).map_err(|_| bad("length out of range"))?;
@@ -883,9 +886,15 @@ mod tests {
                 read_superblock_extension_in(&storage, &sb),
                 read_superblock_extension(&f, &sb)
             );
-            assert_eq!(cache_image_state_in(&storage, &sb), cache_image_state(&f, &sb));
+            assert_eq!(
+                cache_image_state_in(&storage, &sb),
+                cache_image_state(&f, &sb)
+            );
             if let Ok(CacheImageState::Loaded(image)) = cache_image_state(&f, &sb) {
-                assert_eq!(&*image.block_in(&storage).unwrap(), image.block(&f).unwrap());
+                assert_eq!(
+                    &*image.block_in(&storage).unwrap(),
+                    image.block(&f).unwrap()
+                );
             }
         }
     }