diff --git a/re.c b/re.c
index 07a826daa7..5030519fc9 100644
--- a/re.c
+++ b/re.c
@@ -1325,14 +1325,14 @@ rb_backref_set_string(VALUE string, long pos, long len)
  *      r.fixed_encoding?                               #=> true
  *      r.encoding                                      #=> #<Encoding:UTF-8>
  *      r =~ "\u{6666} a"                               #=> 2
- *      r =~ "\xa1\xa2".force_encoding("euc-jp")        #=> ArgumentError
+ *      r =~ "\xa1\xa2".force_encoding("euc-jp")        #=> Encoding::CompatibilityError
  *      r =~ "abc".force_encoding("euc-jp")             #=> 0
  *
  *      r = /\u{6666}/
  *      r.fixed_encoding?                               #=> true
  *      r.encoding                                      #=> #<Encoding:UTF-8>
  *      r =~ "\u{6666} a"                               #=> 0
- *      r =~ "\xa1\xa2".force_encoding("euc-jp")        #=> ArgumentError
+ *      r =~ "\xa1\xa2".force_encoding("euc-jp")        #=> Encoding::CompatibilityError
  *      r =~ "abc".force_encoding("euc-jp")             #=> nil
  */