diff --git a/genlayer_py/abi/calldata/decoder.py b/genlayer_py/abi/calldata/decoder.py
index c993ac8..6d9bb64 100644
--- a/genlayer_py/abi/calldata/decoder.py
+++ b/genlayer_py/abi/calldata/decoder.py
@@ -45,7 +45,7 @@ def impl() -> CalldataEncodable:
         elif typ == consts.TYPE_BYTES:
             ret_bytes = mem[:code]
             mem = mem[code:]
-            return ret_bytes
+            return bytes(ret_bytes)
         elif typ == consts.TYPE_STR:
             ret_str = mem[:code]
             mem = mem[code:]
diff --git a/tests/unit/abi/test_calldata.py b/tests/unit/abi/test_calldata.py
new file mode 100644
index 0000000..78c4d90
--- /dev/null
+++ b/tests/unit/abi/test_calldata.py
@@ -0,0 +1,15 @@
+from genlayer_py.abi import calldata
+
+
+def test_decode_bytes_returns_bytes():
+    decoded = calldata.decode(calldata.encode(b"hello"))
+
+    assert isinstance(decoded, bytes)
+    assert decoded == b"hello"
+
+
+def test_decoded_bytes_round_trip_through_to_str():
+    value = b"hello"
+    decoded = calldata.decode(calldata.encode(value))
+
+    assert calldata.to_str(decoded) == calldata.to_str(value)