diff --git a/lib/logstash/event.rb b/lib/logstash/event.rb
index f4dde9c5b..06a146c0e 100644
--- a/lib/logstash/event.rb
+++ b/lib/logstash/event.rb
@@ -175,6 +175,10 @@ class LogStash::Event
   public
   def overwrite(event)
     @data = event.to_hash
+    #convert timestamp if it is a String
+    if @data["@timestamp"].is_a?(String)
+      @data["@timestamp"] = LogStash::Time.parse_iso8601(@data["@timestamp"])
+    end
   end
 
   public