diff --git a/update_and_deploy_fips.sh b/update_and_deploy_fips.sh
index 9efda9d..3c75fef 100755
--- a/update_and_deploy_fips.sh
+++ b/update_and_deploy_fips.sh
@@ -386,7 +386,7 @@ function indent_of(s,   i,c) {
   }
 
   if (in_udp && line ~ /^[[:space:]]*mtu:[[:space:]]*[0-9]+([[:space:]]*#.*)?$/) {
-    sub(/mtu:[[:space:]]*[0-9]+/, "mtu: 1280", line)
+    line = sprintf("%*smtu: 1280", udp_indent + 2, "")
     udp_has_mtu = 1
   }