diff -r bb11a3aef5b0 Lib/calendar.py
--- a/Lib/calendar.py	Fri Sep 23 11:32:40 2016 +0200
+++ b/Lib/calendar.py	Fri Sep 23 21:11:24 2016 +0800
@@ -124,6 +124,18 @@
     ndays = mdays[month] + (month == February and isleap(year))
     return day1, ndays
 
+class Dummy:
+    """
+    Dummy class to handle extreme dates that can't be represented by
+    datetime.date but we still need them to work properly.
+    """
+
+    def __init__(self, weekday):
+        self.month = 13
+        self._weekday = weekday
+
+    def weekday(self):
+        return self._weekday
 
 class Calendar(object):
     """
@@ -159,7 +171,13 @@
         date = datetime.date(year, month, 1)
         # Go back to the beginning of the week
         days = (date.weekday() - self.firstweekday) % 7
-        date -= datetime.timedelta(days=days)
+        try:
+            date -= datetime.timedelta(days=days)
+        except OverflowError:
+            # Minus days could fail before datetime.MINYEAR
+            weekday = date.weekday()
+            for i in range(days, 0, -1):
+                yield Dummy((weekday - i) % 7)
         oneday = datetime.timedelta(days=1)
         while True:
             yield date
@@ -167,6 +185,11 @@
                 date += oneday
             except OverflowError:
                 # Adding one day could fail after datetime.MAXYEAR
+                weekday = date.weekday()
+                for i in range(1, 7):
+                    if (weekday + i) % 7 == self.firstweekday:
+                        break
+                    yield Dummy((weekday + i) % 7)
                 break
             if date.month != month and date.weekday() == self.firstweekday:
                 break