diff --git a/rc/01-functions.sh b/rc/01-functions.sh
index f11800c..d033d0b 100644
--- a/rc/01-functions.sh
+++ b/rc/01-functions.sh
@@ -95,6 +95,8 @@ function source_try() {
 }
 
 function true_false() {
-  [[ "${1,,}" =~ ^(1|true|yes)$ ]]
+  # lower case and compare
+  # [[ "${1,,}" =~ ^(1|true|yes)$ ]]
+  [[ "${1@L}" =~ ^(1|true|yes)$ ]]
 }