diff --git a/lib/clean/system.sh b/lib/clean/system.sh
index 5960ab5..8ab8488 100644
--- a/lib/clean/system.sh
+++ b/lib/clean/system.sh
@@ -301,7 +301,7 @@ clean_local_snapshots() {
     [[ ${#snapshots[@]} -eq 0 ]] && return 0
     [[ -z "$newest_name" ]] && return 0
 
-    local deletable_count=$(( ${#snapshots[@]} - 1 ))
+    local deletable_count=$((${#snapshots[@]} - 1))
     [[ $deletable_count -le 0 ]] && return 0
 
     if [[ "$DRY_RUN" != "true" ]]; then