diff --git a/ChangeLog b/ChangeLog
index 81f2adf6b4..c6555a67a0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Sep 13 03:44:52 2008  Tanaka Akira  <akr@fsij.org>
+
+	* transcode.c (rb_econv_prepare_opts): raise ArgumentError if
+	  a broken string is specified as a replacement.
+
 Sat Sep 13 03:31:05 2008  Tanaka Akira  <akr@fsij.org>
 
 	* iseq.c (iseq_s_compile_file): use rb_file_open_str.
diff --git a/test/ruby/test_econv.rb b/test/ruby/test_econv.rb
index 4ea2475da0..a26647627a 100644
--- a/test/ruby/test_econv.rb
+++ b/test/ruby/test_econv.rb
@@ -871,4 +871,11 @@ class TestEncodingConverter < Test::Unit::TestCase
     assert_equal([[iso88591,utf8], "universal_newline", [utf8,utf32be]],
                  Encoding::Converter.search_convpath("ISO-8859-1", "UTF-32BE", universal_newline: true))
   end
+
+  def test_invalid_replace
+    assert_raise(ArgumentError) {
+      broken = "\x80".force_encoding("euc-jp")
+      "".encode("euc-jp", :undef => :replace, :replace => broken)
+    }
+  end
 end
diff --git a/transcode.c b/transcode.c
index e7c66ff425..45205dabbd 100644
--- a/transcode.c
+++ b/transcode.c
@@ -2254,7 +2254,6 @@ econv_opts(VALUE opt)
     }
     else if (v==sym_replace) {
         ecflags |= ECONV_INVALID_REPLACE;
-        v = rb_hash_aref(opt, sym_replace);
     }
     else {
         rb_raise(rb_eArgError, "unknown value for invalid character option");
@@ -2315,6 +2314,12 @@ rb_econv_prepare_opts(VALUE opthash, VALUE *opts)
         VALUE v = rb_hash_aref(opthash, sym_replace);
         if (!NIL_P(v)) {
             StringValue(v);
+            if (rb_enc_str_coderange(v) == ENC_CODERANGE_BROKEN) {
+                VALUE dumped = rb_str_dump(v);
+                rb_raise(rb_eArgError, "replacement string is broken: %s as %s",
+                        StringValueCStr(dumped),
+                        rb_enc_name(rb_enc_get(v)));
+            }
             v = rb_str_new_frozen(v);
             newhash = rb_hash_new();
             rb_hash_aset(newhash, sym_replace, v);