diff --git a/ChangeLog b/ChangeLog
index 26b675cfb2..3cab5a6545 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Oct 23 17:55:29 2015  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
+
+	* lib/irb.rb: Ignored assignment of STDOUT.sync = true
+	  when irb.rb loaded. It's affected to IDE such as Jetbrain.
+	  [fix GH-864] Patch by @os97673
+
 Fri Oct 23 16:35:08 2015  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
 
 	* lib/ipaddr.rb, test/test_ipaddr.rb: Reject invalid address contained
diff --git a/lib/irb.rb b/lib/irb.rb
index eb37ecda77..51961db20c 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -18,8 +18,6 @@ require "irb/ruby-lex"
 require "irb/input-method"
 require "irb/locale"
 
-STDOUT.sync = true
-
 # IRB stands for "interactive Ruby" and is a tool to interactively execute Ruby
 # expressions read from the standard input.
 #
@@ -373,6 +371,7 @@ module IRB
 
   # Initializes IRB and creates a new Irb.irb object at the +TOPLEVEL_BINDING+
   def IRB.start(ap_path = nil)
+    STDOUT.sync = true
     $0 = File::basename(ap_path, ".rb") if ap_path
 
     IRB.setup(ap_path)