diff --git a/lib/index.js b/lib/index.js
index c50d581..70fa4cd 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -3,9 +3,10 @@
  * log4js appender support
  */
 const FluentSender = require('fluent-logger');
-const util = require('util');
 const DEFAULT_TAG = 'log4js';
 
+require('es6-object-assign').polyfill();
+
 /**
  *
  * log4js.configure({
@@ -32,8 +33,10 @@ function fluentAppender(config, layout) {
   const logSender = FluentSender.createFluentSender(tag_prefix, options);
 
   const appender = function(loggingEvent) {
-    const data =  util.format.apply(null, loggingEvent.data);
-    const rec = {
+    const data =  loggingEvent.data[0];
+    const extra = loggingEvent.data.splice(1);
+
+    let rec = {
       timestamp: loggingEvent.startTime.getTime(),
       category: loggingEvent.categoryName,
       levelInt: loggingEvent.level.level,
@@ -41,6 +44,11 @@ function fluentAppender(config, layout) {
       context: loggingEvent.context,
       data: data
     };
+
+    if (extra.length > 0) {
+      rec['extra'] = Object.assign.apply(null, extra);
+    }
+
     if (options.levelTag !== false) {
       logSender.emit(loggingEvent.level.levelStr, rec);
     } else {
@@ -50,6 +58,7 @@ function fluentAppender(config, layout) {
   appender.shutdown = (complete) => {
     logSender.end(null, null, complete);
   };
+
   ['addListener', 'on', 'once', 'removeListener', 'removeAllListeners', 'setMaxListeners', 'getMaxListeners', '_setupErrorHandler'].forEach((attr, i) => {
     appender[attr] = function() {
       return logSender[attr].apply(logSender, Array.prototype.slice.call(arguments));
diff --git a/package.json b/package.json
index 88d01e1..4e34f63 100644
--- a/package.json
+++ b/package.json
@@ -20,8 +20,9 @@
     "fluentd"
   ],
   "dependencies": {
-    "log4js": ">= 2",
-    "fluent-logger": ""
+    "es6-object-assign": "^1.1.0",
+    "fluent-logger": "",
+    "log4js": ">= 2"
   },
   "devDependencies": {
     "async": "",
diff --git a/test/test.log4js.js b/test/test.log4js.js
index 821a4f6..1886ee6 100644
--- a/test/test.log4js.js
+++ b/test/test.log4js.js
@@ -118,4 +118,37 @@ describe('log4js-fluent-appender', () => {
     done();
   });
 
+  it('should log extra', (done) => {
+    const tag_prefix = 'tag_prefix';
+    const options = {
+      levelTag: false,
+      host: 'localhost',
+      port: 24224
+    };
+    const fakeSender = {
+      emit: td.function()
+    };
+    td
+      .when(fluentLogger.createFluentSender(tag_prefix, options))
+      .thenReturn(fakeSender);
+    const logger = getLogger(tag_prefix, options);
+
+    logger.info('This is info message!', {extra1: true, extra2: false}, {extra3: true});
+
+    td.verify(fakeSender.emit({
+      timestamp: td.matchers.anything(),
+      category: 'default',
+      levelInt: 20000,
+      levelStr: 'INFO',
+      context: {},
+      data: 'This is info message!',
+      extra: {
+        extra1: true,
+        extra2: false,
+        extra3: true,
+      }
+    }));
+    done();
+  });
+
 });