diff -Nru jam-2.5.original/jam.h jam-2.5/jam.h
--- jam-2.5.original/jam.h	2003-04-23 06:45:51.000000000 +0200
+++ jam-2.5/jam.h	2005-07-01 23:45:53.000000000 +0200
@@ -449,6 +449,10 @@
 # define OSPLAT "OSPLAT=390"
 # endif
 
+# ifdef __amd64__
+# define OSPLAT "OSPLAT=AMD64"
+# endif
+
 # ifndef OSPLAT
 # define OSPLAT ""
 # endif