diff --git a/xCAT-genesis-builder/debian/postinst b/xCAT-genesis-builder/debian/postinst
index 1847f28b1..d2c008085 100644
--- a/xCAT-genesis-builder/debian/postinst
+++ b/xCAT-genesis-builder/debian/postinst
@@ -24,7 +24,7 @@ case "$1" in
         if [ -f "/proc/cmdline" ]; then
             . /etc/profile.d/xcat.sh
             tarch=`uname -m`
-            mknb %{tarch}
+            mknb ${tarch}
         fi
     fi
     ;;