diff --git a/jaildk b/jaildk
index 7fc404e..10c122d 100755
--- a/jaildk
+++ b/jaildk
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-version=1.10
+version=1.11
 
 usage_jaildk() {
     beg=`tput -T ${TERM:-cons25} md`
@@ -196,6 +196,10 @@ jaildk_build() {
         esac
     done
 
+    if test -z "$jail"; then
+        usage_build
+    fi
+
     if test -z "$mode"; then
         mode=start
     fi