Index: Modules/_ctypes/cfield.c
===================================================================
--- Modules/_ctypes/cfield.c	(revision 85158)
+++ Modules/_ctypes/cfield.c	(working copy)
@@ -428,11 +428,11 @@
 #define LOW_BIT(x)  ((x) & 0xFFFF)
 #define NUM_BITS(x) ((x) >> 16)
 
-/* This seems nore a compiler issue than a Windows/non-Windows one */
-#ifdef MS_WIN32
-#  define BIT_MASK(size) ((1 << NUM_BITS(size))-1)
+/* XXX: 0 must be maximum size integer on the platform */
+#ifdef HAVE_LONG_LONG
+#  define BIT_MASK(size) (~((~Py_ULL(0)) << NUM_BITS(size)))
 #else
-#  define BIT_MASK(size) ((1LL << NUM_BITS(size))-1)
+#  define BIT_MASK(size) (~((~0UL) << NUM_BITS(size)))
 #endif
 
 /* This macro CHANGES the first parameter IN PLACE. For proper sign handling,