diff --git a/ChangeLog b/ChangeLog
index d16b8313c8..4ed5cbb89a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Aug 25 12:56:54 2014  Ivan Korunkov  <ivankorunkov@ya.ru>
+
+	* lib/logger.rb (format_datetime): use "%6N" to show microsecond.
+	  [Fix GH-704]
+
 Mon Aug 25 11:02:07 2014  Eric Wong  <e@80x24.org>
 
 	* vm_core.h (rb_iseq_location_t): change first_lineno type to VALUE
diff --git a/lib/logger.rb b/lib/logger.rb
index 14443157cc..9b8bac8e48 100644
--- a/lib/logger.rb
+++ b/lib/logger.rb
@@ -511,7 +511,7 @@ private
 
     def format_datetime(time)
       if @datetime_format.nil?
-        time.strftime("%Y-%m-%dT%H:%M:%S.") << "%06d " % time.usec
+        time.strftime("%Y-%m-%dT%H:%M:%S.%6N ")
       else
         time.strftime(@datetime_format)
       end