Index: Lib/ctypes/test/test_callbacks.py
===================================================================
--- Lib/ctypes/test/test_callbacks.py	(revision 88199)
+++ Lib/ctypes/test/test_callbacks.py	(working copy)
@@ -207,6 +207,37 @@
             windll.user32.EnumWindows(EnumWindowsCallbackFunc, 0)
             self.assertFalse(windowCount == 0)
 
+    def test_callback_register_int(self):
+        dll = CDLL(_ctypes_test.__file__)
+        CALLBACK = CFUNCTYPE(c_int, c_int, c_int, c_int, c_int, c_int)
+        func = dll._testfunc_cbk_reg_int
+        func.argtypes = (c_int, c_int, c_int, c_int, c_int, CALLBACK)
+        func.restype = c_int
+
+        def callback(a, b, c, d, e):
+            return a+b+c+d+e
+
+        result = func(1, 2, 3, 4, 5, CALLBACK(callback))
+        self.assertEqual(result, callback(1*1, 2*2, 3*3, 4*4, 5*5))
+
+
+    def test_callback_register_double(self):
+        dll = CDLL(_ctypes_test.__file__)
+
+        CALLBACK = CFUNCTYPE(c_double, c_double, c_double, c_double,
+                             c_double, c_double)
+        func = dll._testfunc_cbk_reg_double
+        func.argtypes = (c_double, c_double, c_double,
+                         c_double, c_double, CALLBACK)
+        func.restype = c_double
+
+        def callback(a, b, c, d, e):
+            return a+b+c+d+e
+
+        result = func(1.1, 2.2, 3.3, 4.4, 5.5, CALLBACK(callback))
+        self.assertEqual(result, callback(1.1*1.1, 2.2*2.2, 3.3*3.3
+                                          , 4.4*4.4, 5.5*5.5))
+
 ################################################################
 
 if __name__ == '__main__':
Index: Modules/_ctypes/libffi_msvc/ffi.c
===================================================================
--- Modules/_ctypes/libffi_msvc/ffi.c	(revision 88199)
+++ Modules/_ctypes/libffi_msvc/ffi.c	(working copy)
@@ -379,7 +379,7 @@
   short bytes;
   char *tramp;
 #ifdef _WIN64
-  int mask;
+  int mask = 0;
 #endif
   FFI_ASSERT (cif->abi == FFI_SYSV);
   
Index: Modules/_ctypes/_ctypes_test.c
===================================================================
--- Modules/_ctypes/_ctypes_test.c	(revision 88199)
+++ Modules/_ctypes/_ctypes_test.c	(working copy)
@@ -25,6 +25,19 @@
 
 /* some functions handy for testing */
 
+EXPORT(int)
+_testfunc_cbk_reg_int(int a, int b, int c, int d, int e,
+					  int (*func)(int, int, int, int, int))
+{
+    return func(a*a, b*b, c*c, d*d, e*e);
+}
+
+EXPORT(double)
+_testfunc_cbk_reg_double(double a, double b, double c, double d, double e,
+						 double (*func)(double, double, double, double, double))
+{
+	return func(a*a, b*b, c*c, d*d, e*e);
+}
 EXPORT(void)testfunc_array(int values[4])
 {
     printf("testfunc_array %d %d %d %d\n",