diff --git a/deploy/aws_ami/first-time-setup.sh b/deploy/aws_ami/first-time-setup.sh
index aa7c58f818..1299e0915d 100755
--- a/deploy/aws_ami/first-time-setup.sh
+++ b/deploy/aws_ami/first-time-setup.sh
@@ -48,7 +48,7 @@ urlencode() {
     LC_COLLATE=C
 
     local length="${#1}"
-    for (( i = 0; i < length; i++ )); do
+    for (( i = 0; i < $length; i++ )); do
         local c="${1:i:1}"
         case $c in
             [a-zA-Z0-9.~_-]) printf "$c" ;;