diff --git a/ChangeLog b/ChangeLog
index 1134bf7c9c..5a40954f3f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Jan 28 12:32:31 2013  Tanaka Akira  <akr@fsij.org>
+
+	* ext/fcntl/fcntl.c: update document.  use "file descriptor" instead
+	  of "file handle" because it is not used other Ruby documents and
+	  it is confusing with Windows file handle.
+	  correct F_DUPFD behavior.
+
 Sat Jan 26 22:39:12 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* marshal.c (w_object): dump instance variables of the result of
diff --git a/ext/fcntl/fcntl.c b/ext/fcntl/fcntl.c
index 311569c134..3538d94948 100644
--- a/ext/fcntl/fcntl.c
+++ b/ext/fcntl/fcntl.c
@@ -68,15 +68,19 @@ Init_fcntl()
 #ifdef F_DUPFD
     /* Document-const: F_DUPFD
      *
-     * Duplicate a close-on-exec file handle to a non-close-on-exec file
-     * handle.
+     * Duplicate a file descriptor to the mimimum unused file descriptor
+     * greater than or equal to the argument.
+     *
+     * The close-on-exec flag of the duplicated file descriptor is set.
+     * (Ruby uses F_DUPFD_CLOEXEC internally if available to avoid race
+     * condition.  F_SETFD is used if F_DUPFD_CLOEXEC is not available.)
      */
     rb_define_const(mFcntl, "F_DUPFD", INT2NUM(F_DUPFD));
 #endif
 #ifdef F_GETFD
     /* Document-const: F_GETFD
      *
-     * Read the close-on-exec flag of a file handle.
+     * Read the close-on-exec flag of a file descriptor.
      */
     rb_define_const(mFcntl, "F_GETFD", INT2NUM(F_GETFD));
 #endif
@@ -91,7 +95,7 @@ Init_fcntl()
 #ifdef F_SETFD
     /* Document-const: F_SETFD
      *
-     * Set the close-on-exec flag of a file handle.
+     * Set the close-on-exec flag of a file descriptor.
      */
     rb_define_const(mFcntl, "F_SETFD", INT2NUM(F_SETFD));
 #endif
@@ -128,7 +132,7 @@ Init_fcntl()
     rb_define_const(mFcntl, "F_SETLKW", INT2NUM(F_SETLKW));
 #endif
 #ifdef FD_CLOEXEC
-    /* Document-const: F_CLOEXEC
+    /* Document-const: FD_CLOEXEC
      *
      * the value of the close-on-exec flag.
      */