diff --git a/lib/logstash/codecs/fluent.rb b/lib/logstash/codecs/fluent.rb
index 92175f3..73b5ccd 100644
--- a/lib/logstash/codecs/fluent.rb
+++ b/lib/logstash/codecs/fluent.rb
@@ -53,6 +53,10 @@ def encode(event)
 
   private
 
+  def merge_values(source, target)
+      source.merge!(target){|key, old_val, new_val| [new_val, old_val]}
+  end
+
   def decode_event(data, &block)
     tag = data[0]
     entries = data[1]
@@ -70,10 +74,10 @@ def decode_event(data, &block)
       entries_decoder.feed_each(entries) do |entry|
         epochtime = entry[0]
         map = entry[1]
-        event = LogStash::Event.new(map.merge(
-                                      LogStash::Event::TIMESTAMP => LogStash::Timestamp.at(epochtime),
-                                      "tags" => [ tag ]
-                                    ))
+        event = LogStash::Event.new(merge_values(map, {
+          LogStash::Event::TIMESTAMP => LogStash::Timestamp.at(epochtime),
+          "tags" => tag
+        }))
         yield event
       end
     when Array
@@ -81,20 +85,20 @@ def decode_event(data, &block)
       entries.each do |entry|
         epochtime = entry[0]
         map = entry[1]
-        event = LogStash::Event.new(map.merge(
-                                      LogStash::Event::TIMESTAMP => LogStash::Timestamp.at(epochtime),
-                                      "tags" => [ tag ]
-                                    ))
+        event = LogStash::Event.new(merge_values(map, {
+          LogStash::Event::TIMESTAMP => LogStash::Timestamp.at(epochtime),
+          "tags" => tag
+        }))
         yield event
       end
     when Fixnum
       # Message
       epochtime = entries
       map = data[2]
-      event = LogStash::Event.new(map.merge(
-                                    LogStash::Event::TIMESTAMP => LogStash::Timestamp.at(epochtime),
-                                    "tags" => [ tag ]
-                                  ))
+      event = LogStash::Event.new(merge_values(map, {
+        LogStash::Event::TIMESTAMP => LogStash::Timestamp.at(epochtime),
+        "tags" => tag
+      }))
       yield event
     else
       raise(LogStash::Error, "Unknown event type")
diff --git a/spec/codecs/fluent_spec.rb b/spec/codecs/fluent_spec.rb
index c85cd1f..6d0a412 100644
--- a/spec/codecs/fluent_spec.rb
+++ b/spec/codecs/fluent_spec.rb
@@ -38,6 +38,7 @@
     it "should decode without errors" do
       subject.decode(message) do |event|
         expect(event.get("name")).to eq("foo")
+        expect(event.get("tags")).to eq(tag)
       end
     end
 
@@ -63,6 +64,7 @@
 
       subject.decode(message) do |event|
         expect(event.get("name")).to eq("foo")
+        expect(event.get("tags")).to eq(tag)
         count += 1
       end