diff -r 8f4e2080e7a5 Modules/_datetimemodule.c
--- a/Modules/_datetimemodule.c	Tue Jan 03 11:19:48 2017 +0200
+++ b/Modules/_datetimemodule.c	Tue Jan 03 23:44:31 2017 +0100
@@ -49,14 +49,17 @@ class datetime.datetime "PyDateTime_Date
 #define MAX_DELTA_DAYS 999999999

 /* Rename the long macros in datetime.h to more reasonable short names. */
-#define GET_YEAR                PyDateTime_GET_YEAR
-#define GET_MONTH               PyDateTime_GET_MONTH
-#define GET_DAY                 PyDateTime_GET_DAY
-#define DATE_GET_HOUR           PyDateTime_DATE_GET_HOUR
-#define DATE_GET_MINUTE         PyDateTime_DATE_GET_MINUTE
-#define DATE_GET_SECOND         PyDateTime_DATE_GET_SECOND
-#define DATE_GET_MICROSECOND    PyDateTime_DATE_GET_MICROSECOND
-#define DATE_GET_FOLD           PyDateTime_DATE_GET_FOLD
+#define CHECK(o)           assert(PyType_IsSubtype(Py_TYPE(o), &PyDateTime_DateType) || PyType_IsSubtype(Py_TYPE(o), &PyDateTime_DateTimeType))
+#define GET_YEAR(o)             (CHECK(o), PyDateTime_GET_YEAR(o))
+#define GET_MONTH(o)            (CHECK(o), PyDateTime_GET_MONTH(o))
+#define GET_DAY(o)              (CHECK(o), PyDateTime_GET_DAY(o))
+
+#define DATE_CHECK(o)           assert(PyType_IsSubtype(Py_TYPE(o), &PyDateTime_DateType))
+#define DATE_GET_HOUR(o)        (DATE_CHECK(o), PyDateTime_DATE_GET_HOUR(o))
+#define DATE_GET_MINUTE(o)      (DATE_CHECK(o), PyDateTime_DATE_GET_MINUTE(o))
+#define DATE_GET_SECOND(o)      (DATE_CHECK(o), PyDateTime_DATE_GET_SECOND(o))
+#define DATE_GET_MICROSECOND(o) (DATE_CHECK(o), PyDateTime_DATE_GET_MICROSECOND(o))
+#define DATE_GET_FOLD(o)        (DATE_CHECK(o), PyDateTime_DATE_GET_FOLD(o))

 /* Date accessors for date and datetime. */
 #define SET_YEAR(o, v)          (((o)->data[0] = ((v) & 0xff00) >> 8), \
@@ -75,11 +78,12 @@ class datetime.datetime "PyDateTime_Date
 #define DATE_SET_FOLD(o, v)   (PyDateTime_DATE_GET_FOLD(o) = (v))

 /* Time accessors for time. */
-#define TIME_GET_HOUR           PyDateTime_TIME_GET_HOUR
-#define TIME_GET_MINUTE         PyDateTime_TIME_GET_MINUTE
-#define TIME_GET_SECOND         PyDateTime_TIME_GET_SECOND
-#define TIME_GET_MICROSECOND    PyDateTime_TIME_GET_MICROSECOND
-#define TIME_GET_FOLD           PyDateTime_TIME_GET_FOLD
+#define TIME_CHECK(o)           assert(PyType_IsSubtype(Py_TYPE(o), &PyDateTime_TimeType))
+#define TIME_GET_HOUR(o)        (TIME_CHECK(o), PyDateTime_TIME_GET_HOUR(o))
+#define TIME_GET_MINUTE(o)      (TIME_CHECK(o), PyDateTime_TIME_GET_MINUTE(o))
+#define TIME_GET_SECOND(o)      (TIME_CHECK(o), PyDateTime_TIME_GET_SECOND(o))
+#define TIME_GET_MICROSECOND(o) (TIME_CHECK(o), PyDateTime_TIME_GET_MICROSECOND(o))
+#define TIME_GET_FOLD(o)        (TIME_CHECK(o), PyDateTime_TIME_GET_FOLD(o))
 #define TIME_SET_HOUR(o, v)     (PyDateTime_TIME_GET_HOUR(o) = (v))
 #define TIME_SET_MINUTE(o, v)   (PyDateTime_TIME_GET_MINUTE(o) = (v))
 #define TIME_SET_SECOND(o, v)   (PyDateTime_TIME_GET_SECOND(o) = (v))