diff --git a/ab-nginx.sh b/ab-nginx.sh
index 13a0eef..804c710 100755
--- a/ab-nginx.sh
+++ b/ab-nginx.sh
@@ -23,6 +23,9 @@ unset CONFIG_DIR
 unset SERVERS_DIR
 unset WEBROOT_DIR
 unset vmount
+if [ "$TLS13_ONLY" ]; then
+    TLS13_ONLY=$( echo "$TLS13_ONLY" | tr "[:lower:]" "[:upper:]" )
+fi
 
 
 ### functions