diff --git a/ChangeLog b/ChangeLog
index f0f66d756e..60f79b5bcd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Oct  5 11:47:19 2016  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
+
+	* io.c: Fixed equivalent ruby code with core implemention.
+	  [fix GH-1429][ci skip]
+
 Wed Oct  5 11:36:21 2016  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
 
 	* lib/delegate.rb: Added missing spaces and Removed needless spaces.
diff --git a/io.c b/io.c
index 980f8232bf..e50d0d07a0 100644
--- a/io.c
+++ b/io.c
@@ -7276,6 +7276,7 @@ rb_f_p(int argc, VALUE *argv, VALUE self)
  *
  *     def display(port=$>)
  *       port.write self
+ *       nil
  *     end
  *
  *  For example: