diff --git a/msgpack/ext.py b/msgpack/ext.py
index 8341c68b..4eb9dd65 100644
--- a/msgpack/ext.py
+++ b/msgpack/ext.py
@@ -178,7 +178,9 @@ def to_datetime(self):
 
         :rtype: datetime.
         """
-        return datetime.datetime.fromtimestamp(self.to_unix(), _utc)
+        return datetime.datetime.fromtimestamp(0, _utc) + datetime.timedelta(
+            seconds=self.to_unix()
+        )
 
     @staticmethod
     def from_datetime(dt):