diff --git a/tools/archive-images.sh b/tools/archive-images.sh
index 3f6d53c..cad0525 100755
--- a/tools/archive-images.sh
+++ b/tools/archive-images.sh
@@ -20,7 +20,7 @@ patterns=("$@")
 
 for v in "$images_dir" "$archive_dir" "${patterns[@]}"; do
 	case $v in
-		*[\ space\'\"]*) die "unsafe argument (whitespace/quotes): $v" ;;
+		*[[:space:]\'\"]*) die "unsafe argument (whitespace/quotes): $v" ;;
 	esac
 done