Index: Modules/_ctypes/callproc.c
===================================================================
--- Modules/_ctypes/callproc.c	(revision 54879)
+++ Modules/_ctypes/callproc.c	(working copy)
@@ -498,21 +498,28 @@
 
 	if (PyInt_Check(obj)) {
 		pa->ffi_type = &ffi_type_sint;
-		pa->value.i = PyInt_AS_LONG(obj);
+		pa->value.l = PyInt_AS_LONG(obj);
+#if SIZEOF_INT < SIZEOF_LONG
+		if (pa->value.l != pa->value.i) {
+			PyErr_SetString(PyExc_OverflowError,
+					"int is too long to convert");
+			return -1;
+		}
+#endif
 		return 0;
 	}
 
 	if (PyLong_Check(obj)) {
 		pa->ffi_type = &ffi_type_sint;
-		pa->value.i = (long)PyLong_AsUnsignedLong(obj);
-		if (pa->value.i == -1 && PyErr_Occurred()) {
-			PyErr_Clear();
-			pa->value.i = PyLong_AsLong(obj);
-			if (pa->value.i == -1 && PyErr_Occurred()) {
-				PyErr_SetString(PyExc_OverflowError,
-						"long int too long to convert");
-				return -1;
-			}
+		pa->value.l = PyLong_AsLong(obj);
+		if ((pa->value.l == -1 && PyErr_Occurred())
+#if SIZEOF_INT < SIZEOF_LONG
+		    || pa->value.l != pa->value.i
+#endif
+		    ) {
+			PyErr_SetString(PyExc_OverflowError,
+					"long is too long to convert");
+			return -1;
 		}
 		return 0;
 	}
Index: Modules/_ctypes/cfield.c
===================================================================
--- Modules/_ctypes/cfield.c	(revision 54879)
+++ Modules/_ctypes/cfield.c	(working copy)
@@ -356,7 +356,7 @@
 			     v->ob_type->tp_name);
 		return -1;
 	}
-	x = PyInt_AsUnsignedLongMask(v);
+	x = PyInt_AsLong(v);
 	if (x == -1 && PyErr_Occurred())
 		return -1;
 	*p = x;
@@ -564,6 +564,11 @@
 	short x;
 	if (get_long(value, &val) < 0)
 		return NULL;
+	if (val != (short)val) {
+		PyErr_SetString(PyExc_OverflowError,
+				"value is too long for c short");
+		return NULL;
+	}
 	memcpy(&x, ptr, sizeof(x));
 	x = SET(x, (short)val, size);
 	memcpy(ptr, &x, sizeof(x));
@@ -578,6 +583,11 @@
 	short field;
 	if (get_long(value, &val) < 0)
 		return NULL;
+	if (val != (short)val) {
+		PyErr_SetString(PyExc_OverflowError,
+				"value is too long for c short");
+		return NULL;
+	}
 	memcpy(&field, ptr, sizeof(field));
 	field = SWAP_2(field);
 	field = SET(field, (short)val, size);
@@ -660,6 +670,13 @@
 	int x;
 	if (get_long(value, &val) < 0)
 		return NULL;
+#if SIZEOF_INT < SIZEOF_LONG
+	if (val != (int)val) {
+		PyErr_SetString(PyExc_OverflowError,
+				"value is too long for c int");
+		return NULL;
+	}
+#endif
 	memcpy(&x, ptr, sizeof(x));
 	x = SET(x, (int)val, size);
 	memcpy(ptr, &x, sizeof(x));
@@ -673,6 +690,13 @@
 	int field;
 	if (get_long(value, &val) < 0)
 		return NULL;
+#if SIZEOF_INT < SIZEOF_LONG
+	if (val != (int)val) {
+		PyErr_SetString(PyExc_OverflowError,
+				"value is too long for c int");
+		return NULL;
+	}
+#endif
 	memcpy(&field, ptr, sizeof(field));
 	field = SWAP_INT(field);
 	field = SET(field, (int)val, size);