diff --git a/ChangeLog b/ChangeLog
index cb2ace44c4..47b6cb8a67 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Aug 22 14:35:57 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* man/irb.1: remove useless -width option.
+	  [ruby-dev:49767] [Bug #12692]
+
 Mon Aug 22 09:02:56 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* iseq.c (Init_ISeq): undefine allocator of InstructionSequence,
diff --git a/man/irb.1 b/man/irb.1
index 8209120230..62bd714ddc 100644
--- a/man/irb.1
+++ b/man/irb.1
@@ -119,7 +119,7 @@ Sets internal debug level to n (not for popular use)
 .El
 .Pp
 .Sh ENVIRONMENT
-.Bl -tag -width "RUBYLIB_PREFIX" -compact
+.Bl -tag -compact
 .It Ev IRBRC
 .Pp
 .El
@@ -130,7 +130,7 @@ depends on same variables as
 .Xr ruby 1 .
 .Pp
 .Sh FILES
-.Bl -tag -width "RUBYLIB_PREFIX" -compact
+.Bl -tag -compact
 .It Pa ~/.irbrc
 Personal irb initialization.
 .Pp