diff --git a/ChangeLog b/ChangeLog
index 4ee954c57a..6c568514d0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Apr 27 12:34:23 2012  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* ext/dl/cfunc.c (rb_dlcfunc_call): should convert a Bignum value to
+	  unsigned long long on Win64.
+	  [ruby-core:44636][Bug #6364] reported by raylinn@gmail.com (ray linn)
+
 Fri Apr 27 10:58:17 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* test/readline/test_readline.rb (setup): avoid affected by user's
diff --git a/ext/dl/cfunc.c b/ext/dl/cfunc.c
index 70cf6c49fc..de05eb37d7 100644
--- a/ext/dl/cfunc.c
+++ b/ext/dl/cfunc.c
@@ -367,7 +367,11 @@ rb_dlcfunc_call(VALUE self, VALUE ary)
 	    stack[i] = (DLSTACK_TYPE)FIX2LONG(arg);
 	}
 	else if (RB_TYPE_P(arg, T_BIGNUM)) {
+#if SIZEOF_VOIDP == SIZEOF_LONG
 	    stack[i] = (DLSTACK_TYPE)rb_big2ulong_pack(arg);
+#else
+	    stack[i] = (DLSTACK_TYPE)rb_big2ull(arg);
+#endif
 	}
 	else {
 	    Check_Type(arg, T_FIXNUM);