diff --git a/Lib/ctypes/__init__.py b/Lib/ctypes/__init__.py
index 61923b6..3a5c3b5 100644
--- a/Lib/ctypes/__init__.py
+++ b/Lib/ctypes/__init__.py
@@ -133,6 +133,18 @@
 from _ctypes import sizeof, byref, addressof, alignment, resize
 from _ctypes import _SimpleCData
 
+def _check_size(typ, typecode=None):
+    # Check if sizeof(ctypes_type) against struct.calcsize.  This
+    # should protect somewhat against a misconfigured libffi.
+    from struct import calcsize
+    if typecode is None:
+        # Most _type_ codes are the same as used in struct
+        typecode = typ._type_
+    actual, required = sizeof(typ), calcsize(typecode)
+    if actual != required:
+        raise SystemError("sizeof(%s) wrong: %d instead of %d" % \
+                          (typ, actual, required))
+
 class py_object(_SimpleCData):
     _type_ = "O"
     def __repr__(self):
@@ -140,18 +152,23 @@
             return super(py_object, self).__repr__()
         except ValueError:
             return "%s(<NULL>)" % type(self).__name__
+_check_size(py_object, "P")
 
 class c_short(_SimpleCData):
     _type_ = "h"
+_check_size(c_short)
 
 class c_ushort(_SimpleCData):
     _type_ = "H"
+_check_size(c_ushort)
 
 class c_long(_SimpleCData):
     _type_ = "l"
+_check_size(c_long)
 
 class c_ulong(_SimpleCData):
     _type_ = "L"
+_check_size(c_ulong)
 
 if _calcsize("i") == _calcsize("l"):
     # if int and long have the same size, make c_int an alias for c_long
@@ -160,15 +177,19 @@
 else:
     class c_int(_SimpleCData):
         _type_ = "i"
+    _check_size(c_int)
 
     class c_uint(_SimpleCData):
         _type_ = "I"
+    _check_size(c_uint)
 
 class c_float(_SimpleCData):
     _type_ = "f"
+_check_size(c_float)
 
 class c_double(_SimpleCData):
     _type_ = "d"
+_check_size(c_double)
 
 if _calcsize("l") == _calcsize("q"):
     # if long and long long have the same size, make c_longlong an alias for c_long
@@ -177,33 +198,40 @@
 else:
     class c_longlong(_SimpleCData):
         _type_ = "q"
+    _check_size(c_longlong)
 
     class c_ulonglong(_SimpleCData):
         _type_ = "Q"
     ##    def from_param(cls, val):
     ##        return ('d', float(val), val)
     ##    from_param = classmethod(from_param)
+    _check_size(c_ulonglong)
 
 class c_ubyte(_SimpleCData):
     _type_ = "B"
 c_ubyte.__ctype_le__ = c_ubyte.__ctype_be__ = c_ubyte
 # backward compatibility:
 ##c_uchar = c_ubyte
+_check_size(c_ubyte)
 
 class c_byte(_SimpleCData):
     _type_ = "b"
 c_byte.__ctype_le__ = c_byte.__ctype_be__ = c_byte
+_check_size(c_byte)
 
 class c_char(_SimpleCData):
     _type_ = "c"
 c_char.__ctype_le__ = c_char.__ctype_be__ = c_char
+_check_size(c_char)
 
 class c_char_p(_SimpleCData):
     _type_ = "z"
+_check_size(c_char_p, "P")
 
 class c_void_p(_SimpleCData):
     _type_ = "P"
 c_voidp = c_void_p # backwards compatibility (to a bug)
+_check_size(c_void_p)
 
 # This cache maps types to pointers to them.
 _pointer_type_cache = {}