diff --git a/lib/logstash/filters/useragent.rb b/lib/logstash/filters/useragent.rb
index d9a7d34c8..add85bc10 100644
--- a/lib/logstash/filters/useragent.rb
+++ b/lib/logstash/filters/useragent.rb
@@ -69,8 +69,8 @@ class LogStash::Filters::UserAgent < LogStash::Filters::Base
         event[@target] = {} if event[@target].nil?
 
         event[@target]["name"] = ua_data.name
-        event[@target]["os"] = ua_data.os if not ua_data.os.nil?
-        event[@target]["device"] = ua_data.device if not ua_data.device.nil?
+        event[@target]["os"] = ua_data.os.to_s if not ua_data.os.nil?
+        event[@target]["device"] = ua_data.device.to_s if not ua_data.device.nil?
 
         if not ua_data.version.nil?
           ua_version = ua_data.version