diff --git a/logstash/formatter.py b/logstash/formatter.py
index 2b5d618..91cd566 100644
--- a/logstash/formatter.py
+++ b/logstash/formatter.py
@@ -3,6 +3,25 @@
 import socket
 import sys
 from datetime import datetime
+try:
+    from datetime import timezone
+except ImportError:
+    from datetime import timedelta, tzinfo
+
+    class _UTC(tzinfo):
+        def utcoffset(self, dt):
+            return timedelta(0)
+
+        def tzname(self, dt):
+            return 'UTC'
+
+        def dst(self, dt):
+            return timedelta(0)
+
+    UTC = _UTC()
+else:
+    UTC = timezone.utc
+
 try:
     import json
 except ImportError:
@@ -70,7 +89,7 @@ def format_source(cls, message_type, host, path):
 
     @classmethod
     def format_timestamp(cls, time):
-        tstamp = datetime.utcfromtimestamp(time)
+        tstamp = datetime.fromtimestamp(time, UTC)
         return tstamp.strftime("%Y-%m-%dT%H:%M:%S") + ".%03d" % (tstamp.microsecond / 1000) + "Z"
 
     @classmethod