diff --git a/ChangeLog b/ChangeLog
index 1385d18fff..1f97e38b50 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Dec 10 11:25:53 2008  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* re.c (rb_reg_initialize): raise RegexpError when encoding
+	  is dummy encoding. [ruby-dev:37091]
+
 Wed Dec 10 01:28:16 2008  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* common.mk (win32.obj): depend on headers.
diff --git a/re.c b/re.c
index 3a2aa5d362..a45ae47d9f 100644
--- a/re.c
+++ b/re.c
@@ -2312,6 +2312,11 @@ rb_reg_initialize(VALUE obj, const char *s, int len, rb_encoding *enc,
         rb_raise(rb_eTypeError, "already initialized regexp");
     re->ptr = 0;
 
+    if (rb_enc_dummy_p(enc)) {
+	    strcpy(err, "can't make regexp with dummy encoding");
+	    return -1;
+    }
+
     unescaped = rb_reg_preprocess(s, s+len, enc, &fixed_enc, err);
     if (unescaped == Qnil)
         return -1;