diff --git a/pytests/test_dag_cbor.py b/pytests/test_dag_cbor.py
index 9157d29..d589d76 100644
--- a/pytests/test_dag_cbor.py
+++ b/pytests/test_dag_cbor.py
@@ -137,6 +137,25 @@ def test_recursion_limit_exceed_on_nested_maps() -> None:
     assert 'in DAG-CBOR decoding' in str(exc_info.value)
 
 
+def test_dag_cbor_decode_largest_unsigned_int_roundtrip() -> None:
+    data = bytes.fromhex('1bffffffffffffffff')
+
+    decoded_result = libipld.decode_dag_cbor(data)
+    assert decoded_result == 2**64 - 1
+
+    encoded_result = libipld.encode_dag_cbor(decoded_result)
+    assert encoded_result == data
+
+
+def test_dag_cbor_decode_smallest_negative_int_roundtrip() -> None:
+    data = bytes.fromhex('3bffffffffffffffff')
+
+    decoded_result = libipld.decode_dag_cbor(data)
+    assert decoded_result == -(2**64)
+
+    encoded_result = libipld.encode_dag_cbor(decoded_result)
+    assert encoded_result == data
+
 
 def test_dag_cbor_decode_invalid_utf8() -> None:
     with pytest.raises(ValueError) as exc_info:
@@ -160,4 +179,3 @@ def test_dab_cbor_encode_map_int_key() -> None:
         libipld.encode_dag_cbor(obj)
 
     assert 'Map keys must be strings' in str(exc_info.value)
-
diff --git a/src/lib.rs b/src/lib.rs
index 0e2e511..5b4c383 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -130,7 +130,7 @@ fn decode_dag_cbor_to_pyobject<R: Read + Seek>(
     let major = decode::read_major(r)?;
     Ok(match major.kind() {
         MajorKind::UnsignedInt => decode::read_uint(r, major)?.into_pyobject(py)?.into(),
-        MajorKind::NegativeInt => (-1 - decode::read_uint(r, major)? as i64).into_pyobject(py)?.into(),
+        MajorKind::NegativeInt => (-1 - decode::read_uint(r, major)? as i128).into_pyobject(py)?.into(),
         MajorKind::ByteString => {
             let len = decode::read_uint(r, major)?;
             PyBytes::new(py, &decode::read_bytes(r, len)?).into_pyobject(py)?.into()
@@ -239,7 +239,7 @@ fn encode_dag_cbor_from_pyobject<'py, W: Write>(
 
         Ok(())
     } else if obj.is_instance_of::<PyInt>() {
-        let i: i64 = obj.extract()?;
+        let i: i128 = obj.extract()?;
 
         if i.is_negative() {
             encode::write_u64(w, MajorKind::NegativeInt, -(i + 1) as u64)?