diff --git a/eval.c b/eval.c
index 59887bc76a..c4bda48524 100644
--- a/eval.c
+++ b/eval.c
@@ -1505,10 +1505,10 @@ rb_f_callee_name(void)
  *  call-seq:
  *     __dir__         -> string
  *
- *  Returns the absolute path of the directory of the file from which this
- *  method is called.
+ *  Returns the canonicalized absolute path of the directory of the file from
+ *  which this method is called. It means symlinks in the path is resolved.
  *  If <code>__FILE__</code> is <code>nil</code>, it returns <code>nil</code>.
- *  The return value equals to <code>File.dirname(File.expand_path(__FILE__))</code>.
+ *  The return value equals to <code>File.dirname(File.realpath(__FILE__))</code>.
  *
  */
 static VALUE