diff --git a/ChangeLog b/ChangeLog
index 1c60c1f285..981afba581 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Oct 12 18:25:43 2010  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* io.c (rb_io_ungetc): always see Bignum. On 32bit valid value
+	  may be a Bignum. On 64bit for errors. [ruby-dev:42366]
+
 Tue Oct 12 18:25:04 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* string.c (rb_str_concat): use unsigned int for GB18030.
diff --git a/io.c b/io.c
index cb1997a486..21d6d12c9c 100644
--- a/io.c
+++ b/io.c
@@ -3231,11 +3231,9 @@ rb_io_ungetc(VALUE io, VALUE c)
     if (FIXNUM_P(c)) {
 	c = rb_enc_uint_chr(FIX2UINT(c), io_read_encoding(fptr));
     }
-#if SIZEOF_LONG > SIZEOF_INT
     else if (TYPE(c) == T_BIGNUM) {
 	c = rb_enc_uint_chr(NUM2UINT(c), io_read_encoding(fptr));
     }
-#endif
     else {
 	SafeStringValue(c);
     }