diff --git a/pytests/test_dag_cbor.py b/pytests/test_dag_cbor.py
index e8a73d7..fee7708 100644
--- a/pytests/test_dag_cbor.py
+++ b/pytests/test_dag_cbor.py
@@ -246,3 +246,21 @@ def test_decode_dag_cbor_multi() -> None:
     assert len(decoded) == 2
     assert decoded[0] == 0
     assert decoded[1] == 0
+
+
+def test_encode_tag_positive_bignum() -> None:
+    bignum = 18446744073709551616
+
+    with pytest.raises(ValueError) as exc_info:
+         libipld.encode_dag_cbor(bignum)
+
+    assert 'number out of range' in str(exc_info.value).lower()
+
+
+def test_encode_tag_negative_bignum() -> None:
+    bignum = -18446744073709551617
+
+    with pytest.raises(ValueError) as exc_info:
+         libipld.encode_dag_cbor(bignum)
+
+    assert 'number out of range' in str(exc_info.value).lower()
diff --git a/src/lib.rs b/src/lib.rs
index 1d90a91..04f83b3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -254,8 +254,16 @@ fn encode_dag_cbor_from_pyobject<'py, W: Write>(
         let i: i128 = obj.extract()?;
 
         if i.is_negative() {
+            if -(i + 1) > u64::MAX as i128 {
+                return Err(anyhow!("Number out of range"));
+            }
+
             encode::write_u64(w, MajorKind::NegativeInt, -(i + 1) as u64)?
         } else {
+            if i > u64::MAX as i128 {
+                return Err(anyhow!("Number out of range"));
+            }
+
             encode::write_u64(w, MajorKind::UnsignedInt, i as u64)?
         }