Index: Modules/datetimemodule.c
===================================================================
--- Modules/datetimemodule.c	(revision 81610)
+++ Modules/datetimemodule.c	(working copy)
@@ -2125,7 +2125,29 @@
     }
     if (leftover_us) {
         /* Round to nearest whole # of us, and add into x. */
-        PyObject *temp = PyLong_FromLong(round_to_long(leftover_us));
+        double whole_us = round(leftover_us);
+        int x_is_odd;
+        PyObject *temp;
+
+        whole_us = round(leftover_us);
+        if (fabs(whole_us - leftover_us) == 0.5) {
+            /* We're exactly halfway between two integers.  In order to do
+             * round-half-to-even, we must determine whether x is odd. */
+            temp = PyNumber_And(x, us_per_us);
+            if (temp == NULL) {
+                Py_DECREF(x);
+                goto Done;
+            }
+            x_is_odd = PyObject_IsTrue(temp);
+            Py_DECREF(temp);
+            if (x_is_odd == -1) {
+                Py_DECREF(x);
+                goto Done;
+            }
+            whole_us = 2.0 * round((leftover_us + x_is_odd) * 0.5) - x_is_odd;
+        }
+
+        temp = PyLong_FromLong(whole_us);
         if (temp == NULL) {
             Py_DECREF(x);
             goto Done;