diff --git a/create-config-drive b/create-config-drive
index ec0f33c..729e288 100755
--- a/create-config-drive
+++ b/create-config-drive
@@ -48,6 +48,18 @@ done
 config_image=$1
 shift
 
+if [ -z "$config_image" ]; then
+	echo "The imagename argument must be specified!" >&2
+	usage >&2
+	exit 3
+fi
+
+if [ $# -ne 0 ]; then
+	echo "This command requires exactly one positional argument!" >&2
+	usage >&2
+	exit 4
+fi
+
 if [ "$ssh_key" ] && [ -f "$ssh_key" ]; then
 	echo "adding pubkey from $ssh_key"
 	ssh_key_data=$(cat "$ssh_key")
@@ -83,9 +95,9 @@ if [ "$ssh_key_data" ]; then
 fi
 
 echo "generating configuration image at $config_image"
-if ! mkisofs -o $config_image -V cidata -r -J --quiet $config_dir; then
+if ! mkisofs -o "$config_image" -V cidata -r -J --quiet $config_dir; then
 	echo "ERROR: failed to create $config_image" >&2
 	exit 1
 fi
-chmod a+r $config_image
+chmod a+r "$config_image"
 
diff --git a/virt-query b/virt-query
index ed429ea..9bec01c 100755
--- a/virt-query
+++ b/virt-query
@@ -37,8 +37,11 @@ class Domain (object):
         for disk in self.domxml.xpath('/domain/devices/disk'):
             if disk.get('type') == 'file':
                 info = {'type': 'file',
-                        'source': disk.find('source').get('file'),
                         'target': disk.find('target').get('dev')}
+
+                if disk.find('source') is not None:
+                    info['source'] = disk.find('source').get('file')
+
                 yield info
 
     def interfaces(self):
@@ -70,6 +73,10 @@ def main():
 
     if args.what in ['disk', 'disks']:
         for disk in dom.disks():
+            if not 'source' in disk:
+                disk['source'] = ''
+                # This won't break scripts iterating the sources like this:
+                # for disk_path in $(virt-query "$DOMAIN" disks | awk '{print $3}'); do
             print '{type} {target} {source}'.format(**disk)
     elif args.what in ['net', 'interfaces', 'iface']:
         for iface in dom.interfaces():