diff --git a/README.md b/README.md
index 394d7e5..c3632a6 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,7 @@ $ make debug		// debug it via qemu & gdb, you'd start gdb to connect it.
 ```
 ```gdb
 $ gdb tools/system
+(gdb) set arch i386:x86-64 
 (gdb) target remote :1234
 (gdb) b main
 (gdb) c