diff --git a/lib/fluent/plugin/grok.rb b/lib/fluent/plugin/grok.rb
index eef8277..fb0b77e 100644
--- a/lib/fluent/plugin/grok.rb
+++ b/lib/fluent/plugin/grok.rb
@@ -33,6 +33,9 @@ def initialize(plugin, conf)
       if @plugin.respond_to?(:multiline_start_regexp) && @plugin.multiline_start_regexp
         @multiline_start_regexp = Regexp.compile(@plugin.multiline_start_regexp[1..-2])
       end
+      if @plugin.respond_to?(:keep_time_key)
+        @keep_time_key = @plugin.keep_time_key
+      end
     end
 
     def add_patterns_from_file(path)
@@ -68,7 +71,7 @@ def expand_pattern_expression(grok_pattern, conf)
       unless types.empty?
         _conf["types"] = types.map{|subname,type| "#{subname}:#{type}" }.join(",")
       end
-      _conf = _conf.merge("expression" => regexp, "multiline" => @multiline_mode)
+      _conf = _conf.merge("expression" => regexp, "multiline" => @multiline_mode, "keep_time_key" => @keep_time_key)
       config = Fluent::Config::Element.new("parse", nil, _conf, [])
       parser = Fluent::Plugin::RegexpParser.new
       parser.configure(config)
diff --git a/test/test_grok_parser.rb b/test/test_grok_parser.rb
index 2d80e5b..ec5d062 100644
--- a/test/test_grok_parser.rb
+++ b/test/test_grok_parser.rb
@@ -301,6 +301,26 @@ class GrokParserTest < ::Test::Unit::TestCase
     end
   end
 
+  sub_test_case "keep_time_key" do
+    test "true" do
+      d = create_driver(%[
+        keep_time_key true
+        <grok>
+          pattern "%{TIMESTAMP_ISO8601:time}"
+        </grok>
+      ])
+      expected = [
+        { "time" => "2014-01-01T00:00:00+0900" }
+      ]
+      records = []
+      d.instance.parse("Some stuff at 2014-01-01T00:00:00+0900") do |time, record|
+        assert_equal(event_time("2014-01-01T00:00:00+0900"), time)
+        records << record
+      end
+      assert_equal(expected, records)
+    end
+  end
+
   private
 
   def create_driver(conf)