@@ -1,6 +1,6 @@
 import unittest
 import sys
-from ctypes import Structure, Union, sizeof, c_char, c_int, CField
+from ctypes import Structure, Union, sizeof, c_byte, c_char, c_int, CField
 from ._support import Py_TPFLAGS_IMMUTABLETYPE, StructCheckMixin
 
 
@@ -75,6 +75,19 @@ def __init_subclass__(cls, **kwargs):
                                     'ctypes state is not initialized'):
             class Subclass(BrokenStructure): ...
 
+    def test_invalid_byte_size_raises(self):
+        with self.assertRaises(ValueError) as cm:
+            CField(
+                name="a",
+                type=c_byte,
+                byte_size=2, # Wrong size: c_byte is only 1 byte
+                byte_offset=2,
+                index=1,
+                _internal_use=True
+            )
+
+            self.assertIn("does not match type size", str(cm.exception))
+
     def test_max_field_size_gh126937(self):
         # Classes for big structs should be created successfully.
         # (But they most likely can't be instantiated.)