diff --git a/lib/bkctld-check b/lib/bkctld-check
index ec32a2a..990cc8d 100755
--- a/lib/bkctld-check
+++ b/lib/bkctld-check
@@ -70,8 +70,8 @@ check_jail() {
         unset local_warning
     fi
     # reset to default values if missing local value
-    ${local_critical:=${CRITICAL}}
-    ${local_warning:=${WARNING}}
+    : ${local_critical:=${CRITICAL}}
+    : ${local_warning:=${WARNING}}
 
     if [ "${local_critical}" -gt "0" ] && [ "${date_diff}" -gt "${local_critical}" ]; then
         nb_crit=$((nb_crit + 1))