diff --git a/ChangeLog b/ChangeLog
index 1e8caf039b..178aa41b04 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jul 31 17:00:10 2008  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* transcode.c (get_replacement_character): fix: invalid byte sequence
+	  is always replaced "\x00?".
+
 Thu Jul 31 16:37:03 2008  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* test/rubygems/test_gem_ext_configure_builder.rb
diff --git a/transcode.c b/transcode.c
index bc1aec495c..4d9f00f8c2 100644
--- a/transcode.c
+++ b/transcode.c
@@ -136,16 +136,16 @@ get_replacement_character(rb_encoding *enc)
     if (rb_enc_asciicompat(enc)) {
 	return "?";
     }
-    else if (utf16be_encoding = enc) {
+    else if (utf16be_encoding == enc) {
 	return "\x00?";
     }
-    else if (utf16le_encoding = enc) {
+    else if (utf16le_encoding == enc) {
 	return "?\x00";
     }
-    else if (utf32be_encoding = enc) {
+    else if (utf32be_encoding == enc) {
 	return "\x00\x00\x00?";
     }
-    else if (utf32le_encoding = enc) {
+    else if (utf32le_encoding == enc) {
 	return "?\x00\x00\x00";
     }
     else {