diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 1d0c1c5..e8ed79e 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -1552,6 +1552,50 @@
         self.assertEqual(dt1.toordinal(), dt2.toordinal())
         self.assertEqual(dt2.newmeth(-7), dt1.year + dt1.month - 7)
 
+    def test_subclass_alternate_constructors(self):
+        # Test that alternate constructors call the constructor
+        class DateSubclass(self.theclass):
+            def __new__(cls, *args, **kwargs):
+                result = self.theclass.__new__(cls, *args, **kwargs)
+                result.extra = 7
+
+                return result
+
+        args = (2003, 4, 14)
+        d_ord = 731319              # Equivalent ordinal date
+        d_isoformat = '2003-04-14'  # Equivalent isoformat()
+
+        base_d = DateSubclass(*args)
+        self.assertIsInstance(base_d, DateSubclass)
+        self.assertEqual(base_d.extra, 7)
+
+        # Timestamp depends on time zone, so we'll calculate the equivalent here
+        ts = datetime.combine(base_d, time(0)).timestamp()
+
+        test_cases = [
+            ('fromordinal', (d_ord,)),
+            ('fromtimestamp', (ts,)),
+            ('fromisoformat', (d_isoformat,)),
+        ]
+
+        for constr_name, constr_args in test_cases:
+            for base_obj in (DateSubclass, base_d):
+                # Test both the classmethod and method
+                with self.subTest(base_obj_type=type(base_obj),
+                                  constr_name=constr_name):
+                    constr = getattr(base_obj, constr_name)
+
+                    dt = constr(*constr_args)
+
+                    # Test that it creates the right subclass
+                    self.assertIsInstance(dt, DateSubclass)
+
+                    # Test that it's equal to the base object
+                    self.assertEqual(dt, base_d)
+
+                    # Test that it called the constructor
+                    self.assertEqual(dt.extra, 7)
+
     def test_pickling_subclass_date(self):
 
         args = 6, 7, 23
@@ -2420,6 +2464,54 @@
         self.assertEqual(dt2.newmeth(-7), dt1.year + dt1.month +
                                           dt1.second - 7)
 
+    def test_subclass_alternate_constructors_datetime(self):
+        # Test that alternate constructors call the constructor
+        class DateTimeSubclass(self.theclass):
+            def __new__(cls, *args, **kwargs):
+                result = self.theclass.__new__(cls, *args, **kwargs)
+                result.extra = 7
+
+                return result
+
+        args = (2003, 4, 14, 12, 30, 15, 123456)
+        d_isoformat = '2003-04-14T12:30:15.123456'      # Equivalent isoformat()
+        utc_ts = 1050323415.123456                      # UTC timestamp
+
+        base_d = DateTimeSubclass(*args)
+        self.assertIsInstance(base_d, DateTimeSubclass)
+        self.assertEqual(base_d.extra, 7)
+
+        # Timestamp depends on time zone, so we'll calculate the equivalent here
+        ts = base_d.timestamp()
+
+        test_cases = [
+            ('fromtimestamp', (ts,)),
+            # See https://bugs.python.org/issue32417
+            # ('fromtimestamp', (ts, timezone.utc)),
+            ('utcfromtimestamp', (utc_ts,)),
+            ('fromisoformat', (d_isoformat,)),
+            ('strptime', (d_isoformat, '%Y-%m-%dT%H:%M:%S.%f')),
+            ('combine', (date(*args[0:3]), time(*args[3:]))),
+        ]
+
+        for constr_name, constr_args in test_cases:
+            for base_obj in (DateTimeSubclass, base_d):
+                # Test both the classmethod and method
+                with self.subTest(base_obj_type=type(base_obj),
+                                  constr_name=constr_name):
+                    constr = getattr(base_obj, constr_name)
+
+                    dt = constr(*constr_args)
+
+                    # Test that it creates the right subclass
+                    self.assertIsInstance(dt, DateTimeSubclass)
+
+                    # Test that it's equal to the base object
+                    self.assertEqual(dt, base_d.replace(tzinfo=None))
+
+                    # Test that it called the constructor
+                    self.assertEqual(dt.extra, 7)
+
     def test_fromisoformat_datetime(self):
         # Test that isoformat() is reversible
         base_dates = [
diff --git a/Misc/NEWS.d/next/Library/2017-12-23-14-51-46.bpo-32403.CVFapH.rst b/Misc/NEWS.d/next/Library/2017-12-23-14-51-46.bpo-32403.CVFapH.rst
new file mode 100644
index 0000000..f05d346
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-12-23-14-51-46.bpo-32403.CVFapH.rst
@@ -0,0 +1,2 @@
+Improved speed of :class:`datetime.date` and :class:`datetime.datetime`
+alternate constructors.
diff --git a/Misc/NEWS.d/next/Library/2017-12-23-14-54-05.bpo-32404.yJqtlJ.rst b/Misc/NEWS.d/next/Library/2017-12-23-14-54-05.bpo-32404.yJqtlJ.rst
new file mode 100644
index 0000000..5299820
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-12-23-14-54-05.bpo-32404.yJqtlJ.rst
@@ -0,0 +1,2 @@
+Fix bug where :meth:`datetime.datetime.fromtimestamp` did not call __new__
+in :class:`datetime.datetime` subclasses.
diff --git a/Modules/_datetimemodule.c b/Modules/_datetimemodule.c
index e68c7c0..d1f48e5 100644
--- a/Modules/_datetimemodule.c
+++ b/Modules/_datetimemodule.c
@@ -847,6 +847,27 @@
 #define new_date(year, month, day) \
     new_date_ex(year, month, day, &PyDateTime_DateType)
 
+// Forward declaration
+static PyObject * new_datetime_ex(int, int, int, int, int, int, int,
+                                  PyObject*, PyTypeObject*);
+
+/* Create date instance with no range checking, or call subclass constructor */
+static PyObject *
+new_date_subclass_ex(int year, int month, int day, PyObject *cls) {
+    PyObject *result;
+    // We have "fast path" constructors for two subclasses: date and datetime
+    if ((PyTypeObject *)cls == &PyDateTime_DateType) {
+        result = new_date_ex(year, month, day, (PyTypeObject *)cls);
+    } else if ((PyTypeObject *)cls == &PyDateTime_DateTimeType) {
+        result = new_datetime_ex(year, month, day, 0, 0, 0, 0, Py_None,
+                                 (PyTypeObject *)cls);
+    } else {
+        result = PyObject_CallFunction(cls, "iii", year, month, day);
+    }
+
+    return result;
+}
+
 /* Create a datetime instance with no range checking. */
 static PyObject *
 new_datetime_ex2(int year, int month, int day, int hour, int minute,
@@ -894,6 +915,40 @@
     new_datetime_ex2(y, m, d, hh, mm, ss, us, tzinfo, fold, \
                     &PyDateTime_DateTimeType)
 
+static PyObject *
+new_datetime_subclass_fold_ex(int year, int month, int day, int hour, int minute,
+                              int second, int usecond, PyObject *tzinfo,
+                              int fold, PyObject *cls) {
+    PyObject* dt;
+    if ((PyTypeObject*)cls == &PyDateTime_DateTimeType) {
+        // Use the fast path constructor
+        dt = new_datetime(year, month, day, hour, minute, second, usecond,
+                          tzinfo, fold);
+    } else {
+        // Subclass
+        dt = PyObject_CallFunction(cls, "iiiiiiiO",
+                                   year,
+                                   month,
+                                   day,
+                                   hour,
+                                   minute,
+                                   second,
+                                   usecond,
+                                   tzinfo);
+    }
+
+    return dt;
+}
+
+static PyObject *
+new_datetime_subclass_ex(int year, int month, int day, int hour, int minute,
+                              int second, int usecond, PyObject *tzinfo,
+                              PyObject *cls) {
+    return new_datetime_subclass_fold_ex(year, month, day, hour, minute,
+                                         second, usecond, tzinfo, 0,
+                                         cls);
+}
+
 /* Create a time instance with no range checking. */
 static PyObject *
 new_time_ex2(int hour, int minute, int second, int usecond,
@@ -2743,10 +2798,10 @@
     if (_PyTime_localtime(t, &tm) != 0)
         return NULL;
 
-    return PyObject_CallFunction(cls, "iii",
-                                 tm.tm_year + 1900,
-                                 tm.tm_mon + 1,
-                                 tm.tm_mday);
+    return new_date_subclass_ex(tm.tm_year + 1900,
+                                tm.tm_mon + 1,
+                                tm.tm_mday,
+                                cls);
 }
 
 /* Return new date from current time.
@@ -2809,8 +2864,7 @@
                                               ">= 1");
         else {
             ord_to_ymd(ordinal, &year, &month, &day);
-            result = PyObject_CallFunction(cls, "iii",
-                                           year, month, day);
+            result = new_date_subclass_ex(year, month, day, cls);
         }
     }
     return result;
@@ -2845,14 +2899,7 @@
         return NULL;
     }
 
-    PyObject *result;
-    if ( (PyTypeObject*)cls == &PyDateTime_DateType ) {
-        result = new_date_ex(year, month, day, (PyTypeObject*)cls);
-    } else {
-        result = PyObject_CallFunction(cls, "iii", year, month, day);
-    }
-
-    return result;
+    return new_date_subclass_ex(year, month, day, cls);
 }
 
 
@@ -4596,9 +4643,8 @@
                 fold = 1;
         }
     }
-    return new_datetime_ex2(year, month, day, hour,
-                            minute, second, us, tzinfo, fold,
-                            (PyTypeObject *)cls);
+    return new_datetime_subclass_fold_ex(year, month, day, hour, minute,
+                                         second, us, tzinfo, fold, cls);
 }
 
 /* Internal helper.
@@ -4764,17 +4810,16 @@
             else
                 tzinfo = Py_None;
         }
-        result = PyObject_CallFunction(cls, "iiiiiiiO",
-                                       GET_YEAR(date),
-                                       GET_MONTH(date),
-                                       GET_DAY(date),
-                                       TIME_GET_HOUR(time),
-                                       TIME_GET_MINUTE(time),
-                                       TIME_GET_SECOND(time),
-                                       TIME_GET_MICROSECOND(time),
-                                       tzinfo);
-        if (result)
-            DATE_SET_FOLD(result, TIME_GET_FOLD(time));
+        result = new_datetime_subclass_fold_ex(GET_YEAR(date),
+                                               GET_MONTH(date),
+                                               GET_DAY(date),
+                                               TIME_GET_HOUR(time),
+                                               TIME_GET_MINUTE(time),
+                                               TIME_GET_SECOND(time),
+                                               TIME_GET_MICROSECOND(time),
+                                               tzinfo,
+                                               TIME_GET_FOLD(time),
+                                               cls);
     }
     return result;
 }
@@ -4832,23 +4877,8 @@
         return NULL;
     }
 
-    PyObject* dt;
-    if ( (PyTypeObject*)cls == &PyDateTime_DateTimeType ) {
-        // Use the fast path constructor
-        dt = new_datetime(year, month, day, hour, minute, second, microsecond,
-                          tzinfo, 0);
-    } else {
-        // Subclass
-        dt = PyObject_CallFunction(cls, "iiiiiiiO",
-                                       year,
-                                       month,
-                                       day,
-                                       hour,
-                                       minute,
-                                       second,
-                                       microsecond,
-                                       tzinfo);
-    }
+    PyObject *dt = new_datetime_subclass_ex(year, month, day, hour, minute,
+                                            second, microsecond, tzinfo, cls);
 
     Py_DECREF(tzinfo);
     return dt;