diff --git a/crates/clawhdf5-format/fuzz/corpus/fuzz_datatype/seed_complex_f64_hdf5_2_0 b/crates/clawhdf5-format/fuzz/corpus/fuzz_datatype/seed_complex_f64_hdf5_2_0
new file mode 100644
index 0000000..5a2bc92
Binary files /dev/null and b/crates/clawhdf5-format/fuzz/corpus/fuzz_datatype/seed_complex_f64_hdf5_2_0 differ
diff --git a/crates/clawhdf5-format/fuzz/corpus/fuzz_datatype/seed_compound_v1_default_libver b/crates/clawhdf5-format/fuzz/corpus/fuzz_datatype/seed_compound_v1_default_libver
new file mode 100644
index 0000000..6595d3a
Binary files /dev/null and b/crates/clawhdf5-format/fuzz/corpus/fuzz_datatype/seed_compound_v1_default_libver differ
diff --git a/crates/clawhdf5-format/src/datatype.rs b/crates/clawhdf5-format/src/datatype.rs
index 40b186e..19242c0 100644
--- a/crates/clawhdf5-format/src/datatype.rs
+++ b/crates/clawhdf5-format/src/datatype.rs
@@ -372,7 +372,8 @@ impl Datatype {
                         pos += name_len;
                         let byte_offset = read_uint(data, pos, ob)?;
                         pos += ob;
-                        let (member_dt, consumed) = Self::parse_with_depth(&data[pos..], depth + 1)?;
+                        let (member_dt, consumed) =
+                            Self::parse_with_depth(&data[pos..], depth + 1)?;
                         pos += consumed;
                         members.push(CompoundMember {
                             name,
@@ -381,24 +382,29 @@ impl Datatype {
                         });
                     }
                 } else if version == 1 || version == 2 {
-                    // v1/v2: name, offset(4), dimensionality(1), reserved(3), dim_perm(4),
-                    //         reserved_dims(up to 4*4=16), member datatype
+                    // v1/v2: name (null-terminated, padded to a multiple of 8
+                    // bytes), offset(4), member datatype. v1 additionally
+                    // carries the legacy per-member array fields between the
+                    // offset and the member datatype: dimensionality(1),
+                    // reserved(3), dim_perm(4), reserved(4), 4 dim sizes(16).
+                    // v1 is what default (non-`latest`) libver bounds emit.
                     for _ in 0..num_members {
                         let (name, name_len) = read_null_terminated_string(data, pos)?;
-                        pos += name_len;
-                        // v1: names padded to 8-byte boundary
-                        if version == 1 {
-                            let total_name_bytes = name_len;
-                            let padded = (total_name_bytes + 7) & !7;
-                            pos = pos - name_len + padded;
-                        }
+                        let padded = name_len.checked_add(7).ok_or(FormatError::UnexpectedEof {
+                            expected: usize::MAX,
+                            available: data.len(),
+                        })? & !7;
+                        ensure_len(data, pos, padded)?;
+                        pos += padded;
                         ensure_len(data, pos, 4)?;
                         let byte_offset = LittleEndian::read_u32(&data[pos..pos + 4]) as u64;
                         pos += 4;
-                        // dimensionality(1) + reserved(3) + dim_perm(4) + 4 dim slots(16) = 24
-                        ensure_len(data, pos, 24)?;
-                        pos += 24;
-                        let (member_dt, consumed) = Self::parse_with_depth(&data[pos..], depth + 1)?;
+                        if version == 1 {
+                            ensure_len(data, pos, 28)?;
+                            pos += 28;
+                        }
+                        let (member_dt, consumed) =
+                            Self::parse_with_depth(&data[pos..], depth + 1)?;
                         pos += consumed;
                         members.push(CompoundMember {
                             name,
@@ -1138,6 +1144,82 @@ mod tests {
         }
     }
 
+    /// Real datatype message bytes emitted by h5py 3.16 / HDF5 2.0 with
+    /// *default* libver bounds for [('x','f8'),('y','f8'),('id','i4')]:
+    /// compound datatype version 1 (padded names + 28 bytes of legacy
+    /// per-member array fields).
+    fn compound_v1_bytes() -> Vec<u8> {
+        let f64le: [u8; 20] = [
+            0x11, 0x20, 0x3f, 0x00, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x34, 0x0b,
+            0x00, 0x34, 0xff, 0x03, 0x00, 0x00,
+        ];
+        let i32le: [u8; 12] = [
+            0x10, 0x08, 0x00, 0x00, 0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x20, 0x00,
+        ];
+        let mut b = vec![0x16, 0x03, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00];
+        for (name, offset, dt) in [
+            (&b"x"[..], 0u32, &f64le[..]),
+            (&b"y"[..], 8, &f64le[..]),
+            (&b"id"[..], 16, &i32le[..]),
+        ] {
+            let mut padded = name.to_vec();
+            padded.resize((name.len() + 1 + 7) & !7, 0);
+            b.extend_from_slice(&padded);
+            b.extend_from_slice(&offset.to_le_bytes());
+            b.extend_from_slice(&[0u8; 28]);
+            b.extend_from_slice(dt);
+        }
+        b
+    }
+
+    fn assert_xyid_compound(dt: Datatype) {
+        match dt {
+            Datatype::Compound { size, members } => {
+                assert_eq!(size, 20);
+                let got: Vec<(&str, u64, u32)> = members
+                    .iter()
+                    .map(|m| (m.name.as_str(), m.byte_offset, m.datatype.type_size()))
+                    .collect();
+                assert_eq!(got, vec![("x", 0, 8), ("y", 8, 8), ("id", 16, 4)]);
+            }
+            other => panic!("expected Compound, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn test_compound_v1_default_libver() {
+        let bytes = compound_v1_bytes();
+        let (dt, consumed) = Datatype::parse(&bytes).unwrap();
+        assert_eq!(consumed, bytes.len());
+        assert_xyid_compound(dt);
+    }
+
+    #[test]
+    fn test_compound_v2_padded_names_no_array_fields() {
+        // v2 = v1 without the 28 bytes of per-member array fields; names are
+        // still padded to a multiple of 8 (matches libhdf5's H5O decoder).
+        let v1 = compound_v1_bytes();
+        let mut v2 = vec![0x26, 0x03, 0x00, 0x00, 0x14, 0x00, 0x00, 0x00];
+        let mut pos = 8;
+        for dt_len in [20usize, 20, 12] {
+            v2.extend_from_slice(&v1[pos..pos + 8 + 4]); // padded name + offset
+            pos += 8 + 4 + 28;
+            v2.extend_from_slice(&v1[pos..pos + dt_len]);
+            pos += dt_len;
+        }
+        let (dt, consumed) = Datatype::parse(&v2).unwrap();
+        assert_eq!(consumed, v2.len());
+        assert_xyid_compound(dt);
+    }
+
+    #[test]
+    fn test_compound_v1_truncated_is_error_not_panic() {
+        let bytes = compound_v1_bytes();
+        for cut in 8..bytes.len() {
+            assert!(Datatype::parse(&bytes[..cut]).is_err(), "cut at {cut}");
+        }
+    }
+
     /// Real datatype message bytes emitted by HDF5 2.0 for the native complex
     /// type `H5T_COMPLEX_IEEE_F64LE`: class 11, version 5, size 16, followed by
     /// the base IEEE f64 datatype message.
@@ -1172,7 +1254,9 @@ mod tests {
         // Compound { z: complex f64 @0, k: i64 @16 } as written by HDF5 2.0.
         // Regression guard: the complex member must consume exactly its own
         // bytes so the following member parses.
-        let mut bytes = vec![0x56, 0x02, 0x00, 0x00, 0x18, 0x00, 0x00, 0x00, b'z', 0x00, 0x00];
+        let mut bytes = vec![
+            0x56, 0x02, 0x00, 0x00, 0x18, 0x00, 0x00, 0x00, b'z', 0x00, 0x00,
+        ];
         bytes.extend_from_slice(&COMPLEX_F64_HDF5_2_0);
         bytes.extend_from_slice(&[b'k', 0x00, 0x10]);
         bytes.extend_from_slice(&[
@@ -1188,7 +1272,10 @@ mod tests {
                     &members[0].datatype,
                     Datatype::Compound { size: 16, members } if members.len() == 2
                 ));
-                assert_eq!((members[1].name.as_str(), members[1].byte_offset), ("k", 16));
+                assert_eq!(
+                    (members[1].name.as_str(), members[1].byte_offset),
+                    ("k", 16)
+                );
             }
             other => panic!("expected Compound, got {other:?}"),
         }
diff --git a/crates/clawhdf5-format/tests/writer_h5py_tests.rs b/crates/clawhdf5-format/tests/writer_h5py_tests.rs
index 7506717..58d1660 100644
--- a/crates/clawhdf5-format/tests/writer_h5py_tests.rs
+++ b/crates/clawhdf5-format/tests/writer_h5py_tests.rs
@@ -235,17 +235,31 @@ fn h5py_reads_our_array_dataset() {
 #[test]
 #[ignore = "requires Python h5py module"]
 fn read_h5py_generated_compound() {
-    let path = std::env::temp_dir().join("clawhdf5_h5py_compound.h5");
+    check_h5py_generated_compound("latest", ", libver='latest'");
+}
+
+/// Same file written with h5py's default format bounds. HDF5 2.0 raised the
+/// default low bound to 1.8, so "default" files exercise different on-disk
+/// structures than both `libver='latest'` and pre-2.0 defaults.
+#[test]
+#[ignore = "requires Python h5py module"]
+fn read_h5py_generated_compound_default_libver() {
+    check_h5py_generated_compound("default", "");
+}
+
+fn check_h5py_generated_compound(tag: &str, libver_kw: &str) {
+    let path = std::env::temp_dir().join(format!("clawhdf5_h5py_compound_{tag}.h5"));
     let gen_script = format!(
         r#"
 import h5py, numpy as np
 dt = np.dtype([('x', 'f8'), ('y', 'f8'), ('id', 'i4')])
 data = np.array([(1.0, 2.0, 10), (3.0, 4.0, 20)], dtype=dt)
-f = h5py.File('{}', 'w', libver='latest')
+f = h5py.File('{}', 'w'{})
 f.create_dataset('particles', data=data)
 f.close()
 "#,
-        path.display()
+        path.display(),
+        libver_kw
     );
     h5py_read(&path, &gen_script);
 
@@ -363,17 +377,31 @@ else:
 #[test]
 #[ignore = "requires Python h5py module"]
 fn read_h5py_generated_enum() {
-    let path = std::env::temp_dir().join("clawhdf5_h5py_enum.h5");
+    check_h5py_generated_enum("latest", ", libver='latest'");
+}
+
+/// Same file written with h5py's default format bounds. HDF5 2.0 raised the
+/// default low bound to 1.8, so "default" files exercise different on-disk
+/// structures than both `libver='latest'` and pre-2.0 defaults.
+#[test]
+#[ignore = "requires Python h5py module"]
+fn read_h5py_generated_enum_default_libver() {
+    check_h5py_generated_enum("default", "");
+}
+
+fn check_h5py_generated_enum(tag: &str, libver_kw: &str) {
+    let path = std::env::temp_dir().join(format!("clawhdf5_h5py_enum_{tag}.h5"));
     let gen_script = format!(
         r#"
 import h5py, numpy as np
 dt = h5py.enum_dtype({{"RED": 0, "GREEN": 1, "BLUE": 2}}, basetype=np.int32)
 data = np.array([1, 0, 2, 1], dtype=np.int32)
-f = h5py.File('{}', 'w', libver='latest')
+f = h5py.File('{}', 'w'{})
 f.create_dataset('colors', data=data, dtype=dt)
 f.close()
 "#,
-        path.display()
+        path.display(),
+        libver_kw
     );
     h5py_read(&path, &gen_script);