diff -r ce67f965a37d Lib/datetime.py
--- a/Lib/datetime.py	Sun Mar 08 09:42:40 2015 -0400
+++ b/Lib/datetime.py	Sun Mar 08 16:43:58 2015 +0100
@@ -1394,8 +1394,8 @@
     @classmethod
     def utcfromtimestamp(cls, t):
         """Construct a naive UTC datetime from a POSIX timestamp."""
-        t, frac = divmod(t, 1.0)
-        us = int(frac * 1e6)
+        t, frac = divmod(t, 1)
+        us = int(frac * 1000000)    # long form required for decimal support
 
         # If timestamp is less than one microsecond smaller than a
         # full second, us can be rounded up to 1000000.  In this case,
diff -r ce67f965a37d Lib/test/datetimetester.py
--- a/Lib/test/datetimetester.py	Sun Mar 08 09:42:40 2015 -0400
+++ b/Lib/test/datetimetester.py	Sun Mar 08 16:43:58 2015 +0100
@@ -1807,6 +1807,8 @@
         expected = time.gmtime(ts)
         got = self.theclass.utcfromtimestamp(ts)
         self.verify_field_equality(expected, got)
+        got = self.theclass.utcfromtimestamp(decimal.Decimal(ts))
+        self.verify_field_equality(expected, got)
 
     # Run with US-style DST rules: DST begins 2 a.m. on second Sunday in
     # March (M3.2.0) and ends 2 a.m. on first Sunday in November (M11.1.0).