--- src/nasm.inc.orig	2009-05-28 16:04:35 +0100
+++ src/nasm.inc	2010-11-27 10:51:04 +0000
@@ -157,9 +157,10 @@
 %define XVID_MOVSXD movsx
 %endif
 
-
-%ifdef WINDOWS
-      %define PREFIX
+%ifndef ARCH_IS_X86_64
+      %ifdef WINDOWS
+            %define PREFIX
+      %endif
 %endif
 
 %ifdef NO_PREFIX
