diff --git a/ChangeLog b/ChangeLog
index 4c0444fd46..a07bb1de5f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Dec 21 15:16:00 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* encoding.c (rb_to_encoding_index): should return error instead of
+	  exception even if type is incorrect.
+
 Fri Dec 21 14:58:27 2007  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* enumerator.c (enumerator_init_copy): prohibit cloning of
diff --git a/encoding.c b/encoding.c
index ba83837f49..819ac54071 100644
--- a/encoding.c
+++ b/encoding.c
@@ -81,6 +81,9 @@ rb_to_encoding_index(VALUE enc)
     if (idx >= 0) {
 	return idx;
     }
+    else if (NIL_P(enc = rb_check_string_type(enc))) {
+	return -1;
+    }
     else {
 	return rb_enc_find_index(StringValueCStr(enc));
     }