diff --git a/crates/clawhdf5-format/src/btree_v2.rs b/crates/clawhdf5-format/src/btree_v2.rs
index 7582c05..d3f6250 100644
--- a/crates/clawhdf5-format/src/btree_v2.rs
+++ b/crates/clawhdf5-format/src/btree_v2.rs
@@ -355,6 +355,23 @@ fn read_internal_node(
         pos += total_nrec_width; // skip total records in subtree
         children.push((addr, child_nrec));
     }
+
+    // The checksum follows the child pointers and covers the node up to it.
+    // Lookups prune children by the keys in this node, so an unverified
+    // internal node could hide a record without any error: libhdf5 refuses
+    // a mismatch here, and so does this.
+    #[cfg(feature = "checksum")]
+    {
+        ensure_len(file_data, pos, 4)?;
+        let stored = LittleEndian::read_u32(&file_data[pos..pos + 4]);
+        let computed = crate::checksum::jenkins_lookup3(&file_data[offset..pos]);
+        if computed != stored {
+            return Err(FormatError::ChecksumMismatch {
+                expected: stored,
+                computed,
+            });
+        }
+    }
     Ok((records_start, children))
 }
 
@@ -733,6 +750,8 @@ mod tests {
             buf.extend_from_slice(&child_nrec.to_le_bytes()[..nrec_width]);
             buf.resize(buf.len() + total_width, 0);
         }
+        let sum = crate::checksum::jenkins_lookup3(&buf);
+        buf.extend_from_slice(&sum.to_le_bytes());
         buf
     }
 
diff --git a/crates/clawhdf5/tests/indexed_lookup_interop.rs b/crates/clawhdf5/tests/indexed_lookup_interop.rs
index 30adb0c..71f48f0 100644
--- a/crates/clawhdf5/tests/indexed_lookup_interop.rs
+++ b/crates/clawhdf5/tests/indexed_lookup_interop.rs
@@ -411,3 +411,87 @@ fn links_of_every_kind_resolve_by_name_as_in_h5py() {
         }
     }
 }
+
+/// The link name index (v2 B-tree, record type 5) of the big group: its
+/// depth and root node address, read from the one type-5 `BTHD` in the file.
+fn name_index_root(bytes: &[u8]) -> (u16, usize) {
+    let headers: Vec<usize> = bytes
+        .windows(4)
+        .enumerate()
+        .filter(|(i, w)| *w == b"BTHD" && bytes.get(i + 5) == Some(&5))
+        .map(|(i, _)| i)
+        .collect();
+    assert_eq!(headers.len(), 1, "type-5 B-tree headers at {headers:?}");
+    let h = headers[0];
+    // signature, version, type, node size (4), record size (2), depth (2),
+    // split and merge percent, root address (8).
+    let depth = u16::from_le_bytes([bytes[h + 12], bytes[h + 13]]);
+    let root = u64::from_le_bytes(bytes[h + 16..h + 24].try_into().unwrap());
+    (depth, usize::try_from(root).unwrap())
+}
+
+/// One byte changed in a key of the name index's root (an internal node)
+/// must be an error, not a name quietly routed to the wrong child and
+/// reported missing: lookups prune children by those keys. libhdf5 checks
+/// the internal node's checksum and refuses the group; so must we, for a
+/// lookup and for a listing.
+#[test]
+fn a_corrupt_internal_index_node_is_an_error_not_a_missing_name() {
+    skip_if_no_python!();
+    let fx = fixture();
+    let mut bytes = std::fs::read(&fx.path).unwrap();
+    let (depth, root) = name_index_root(&bytes);
+    assert!(depth >= 2, "want a deep index, got depth {depth}");
+    assert_eq!(&bytes[root..root + 4], b"BTIN");
+    // Signature, version, type, then record 0: its name hash comes first.
+    bytes[root + 6] ^= 0x5a;
+    let dir = tempfile::tempdir().unwrap();
+    let bad = dir.path().join("bad.h5");
+    std::fs::write(&bad, &bytes).unwrap();
+    let bad = bad.display().to_string();
+
+    let is_checksum = |e: &clawhdf5::Error| {
+        matches!(
+            e,
+            clawhdf5::Error::Format(FormatError::ChecksumMismatch { .. })
+        )
+    };
+    let f = File::open(&bad).unwrap();
+    let g = f.group("g").unwrap();
+    // Every name, present or not, goes through the root.
+    for name in fx.links.keys().step_by(97).chain(&fx.missing_links) {
+        let err = g.dataset(name).map(|_| ()).unwrap_err();
+        assert!(is_checksum(&err), "dataset({name:?}): {err:?}");
+    }
+    let err = f.dataset("/g/n0").map(|_| ()).unwrap_err();
+    assert!(is_checksum(&err), "path: {err:?}");
+    let err = g.datasets().unwrap_err();
+    assert!(is_checksum(&err), "listing: {err:?}");
+    let err = g.entries().unwrap_err();
+    assert!(is_checksum(&err), "entries: {err:?}");
+
+    let m = MmapFile::open(&bad).unwrap();
+    let mg = m.group("g").unwrap();
+    assert!(mg.dataset("n0").is_err_and(|e| is_checksum(&e)));
+    assert!(mg.datasets().is_err_and(|e| is_checksum(&e)));
+    let l = LazyFile::open_mmap(&bad).unwrap();
+    let lg = l.group("g").unwrap();
+    assert!(lg.dataset("n0").is_err_and(|e| is_checksum(&e)));
+    assert!(lg.datasets().is_err_and(|e| is_checksum(&e)));
+
+    // libhdf5 refuses both too.
+    let out = run_python(&format!(
+        "import h5py\n\
+         r = []\n\
+         with h5py.File(r'{bad}', 'r') as f:\n\
+         \x20   g = f['g']\n\
+         \x20   for op in (lambda: g['n0'], lambda: list(g)):\n\
+         \x20       try:\n\
+         \x20           op()\n\
+         \x20           r.append('ok')\n\
+         \x20       except Exception as e:\n\
+         \x20           r.append('checksum' if 'checksum' in str(e) else repr(e))\n\
+         print(' '.join(r))",
+    ));
+    assert_eq!(out, "checksum checksum");
+}