diff --git a/ChangeLog b/ChangeLog
index 47ed4db6b8..f268ae3177 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Nov 16 13:51:40 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* bignum.c (rb_big2ulong): need to calc in unsigned long, because
+	  the range of VALUE is larger than it on LLP64 platform, such as Win64.
+	  this change fixes the failures of test/-ext-/num2int.
+
 Wed Nov 16 12:02:47 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* test/webrick/test_cgi.rb (TestWEBrickCGI#start_cgi_server): there are
diff --git a/bignum.c b/bignum.c
index a1c4ac78a0..2d61bb37c0 100644
--- a/bignum.c
+++ b/bignum.c
@@ -1210,11 +1210,11 @@ rb_big2ulong(VALUE x)
     VALUE num = big2ulong(x, "unsigned long", TRUE);
 
     if (!RBIGNUM_SIGN(x)) {
-	VALUE v = (VALUE)(-(SIGNED_VALUE)num);
+	unsigned long v = (unsigned long)(-(long)num);
 
 	if (v <= LONG_MAX)
 	    rb_raise(rb_eRangeError, "bignum out of range of unsigned long");
-	return v;
+	return (VALUE)v;
     }
     return num;
 }