diff --git a/setup.sh b/setup.sh
index b1a915b..51ed154 100644
--- a/setup.sh
+++ b/setup.sh
@@ -92,7 +92,7 @@ function we_have_exactly_one_part () {
 }
 
 function get_drive_id () {
-    declare drive_id
+    local drive_id
     drive_id="$(find -L /dev/disk/by-id -samefile "${1:?}")"
     if [[ "$(wc -l <<<"${drive_id}")" -eq '1' ]] && [[ "$(wc -c <<<"${drive_id}")" -gt '1' ]]; then
         printf -- '%s' "${drive_id}"