diff --git a/hathor/nanocontracts/nc_types/sized_int_nc_type.py b/hathor/nanocontracts/nc_types/sized_int_nc_type.py
index 1674135a6..d19812e5d 100644
--- a/hathor/nanocontracts/nc_types/sized_int_nc_type.py
+++ b/hathor/nanocontracts/nc_types/sized_int_nc_type.py
@@ -44,12 +44,12 @@ def _upper_bound_value(self) -> int | None:
 
     @classmethod
     def _lower_bound_value(self) -> int | None:
-        if not self._signed:
-            return 0
-        if self._byte_size is not None:
-            return -(2**self._byte_size)
-        else:
+        if self._byte_size is None:
             return None
+        if self._signed:
+            return -(2**(self._byte_size * 8 - 1))
+        else:
+            return 0
 
     @override
     @classmethod
diff --git a/tests/serialization/__init__.py b/tests/serialization/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/serialization/test_sized_int.py b/tests/serialization/test_sized_int.py
new file mode 100644
index 000000000..e83d504f2
--- /dev/null
+++ b/tests/serialization/test_sized_int.py
@@ -0,0 +1,104 @@
+import struct
+
+
+def _test_bounds_struct_pack(fmt: str, lower_bound: int, upper_bound: int) -> None:
+    struct.pack(fmt, lower_bound)
+    try:
+        struct.pack(fmt, lower_bound - 1)
+    except struct.error:
+        pass
+    else:
+        assert False
+    struct.pack(fmt, upper_bound)
+    try:
+        struct.pack(fmt, upper_bound + 1)
+    except struct.error:
+        pass
+    else:
+        assert False
+
+
+def test_int8_bounds() -> None:
+    from hathor.nanocontracts.nc_types.sized_int_nc_type import _SizedIntNCType
+
+    class Int8NCType(_SizedIntNCType):
+        _signed = True
+        _byte_size = 1
+
+    lower_bound = Int8NCType._lower_bound_value()
+    upper_bound = Int8NCType._upper_bound_value()
+
+    assert lower_bound == -128
+    assert upper_bound == 127
+
+    _test_bounds_struct_pack('b', lower_bound, upper_bound)
+
+
+def test_uint8_bounds() -> None:
+    from hathor.nanocontracts.nc_types.sized_int_nc_type import _SizedIntNCType
+
+    class Uint8NCType(_SizedIntNCType):
+        _signed = False
+        _byte_size = 1
+
+    lower_bound = Uint8NCType._lower_bound_value()
+    upper_bound = Uint8NCType._upper_bound_value()
+
+    assert lower_bound == 0
+    assert upper_bound == 255
+
+    _test_bounds_struct_pack('B', lower_bound, upper_bound)
+
+
+def test_int32_bounds() -> None:
+    from hathor.nanocontracts.nc_types.sized_int_nc_type import Int32NCType
+
+    lower_bound = Int32NCType._lower_bound_value()
+    upper_bound = Int32NCType._upper_bound_value()
+
+    assert lower_bound == -2147483648
+    assert upper_bound == 2147483647
+
+    _test_bounds_struct_pack('i', lower_bound, upper_bound)
+
+
+def test_uint32_bounds() -> None:
+    from hathor.nanocontracts.nc_types.sized_int_nc_type import Uint32NCType
+
+    lower_bound = Uint32NCType._lower_bound_value()
+    upper_bound = Uint32NCType._upper_bound_value()
+    assert lower_bound == 0
+    assert upper_bound == 4294967295
+    _test_bounds_struct_pack('I', lower_bound, upper_bound)
+
+
+def test_int64_bounds() -> None:
+    from hathor.nanocontracts.nc_types.sized_int_nc_type import _SizedIntNCType
+
+    class Int64NCType(_SizedIntNCType):
+        _signed = True
+        _byte_size = 8
+
+    lower_bound = Int64NCType._lower_bound_value()
+    upper_bound = Int64NCType._upper_bound_value()
+
+    assert lower_bound == -9223372036854775808
+    assert upper_bound == 9223372036854775807
+
+    _test_bounds_struct_pack('q', lower_bound, upper_bound)
+
+
+def test_uint64_bounds() -> None:
+    from hathor.nanocontracts.nc_types.sized_int_nc_type import _SizedIntNCType
+
+    class Uint64NCType(_SizedIntNCType):
+        _signed = False
+        _byte_size = 8
+
+    lower_bound = Uint64NCType._lower_bound_value()
+    upper_bound = Uint64NCType._upper_bound_value()
+
+    assert lower_bound == 0
+    assert upper_bound == 18446744073709551615
+
+    _test_bounds_struct_pack('Q', lower_bound, upper_bound)