diff --git a/src/options.sh b/src/options.sh
index 48989d4..9b35c0a 100644
--- a/src/options.sh
+++ b/src/options.sh
@@ -9,7 +9,7 @@ do
     c) config_path="$OPTARG" ;;
     f) opt_f=y ;;
     R) opt_R=y ;;
-    *) echo "Unknown option: $OPTARG" >&2 ; usage ; exit 1 ;;
+    \?) echo "Unknown option: $OPTARG" >&2 ; usage ; exit 1 ;;
     esac
 done