--- xdg-su.orig	2012-12-05 20:04:08.040808857 +0100
+++ xdg-su	2012-12-05 20:13:42.972761364 +0100
@@ -59,6 +59,8 @@ Options
 
 -u user
     run command as user. The default is to run as root.
+-c command
+    specifies the command to run. It has to be passed in one argument.
 --help
     Show command synopsis.
 --manual
@@ -398,6 +400,8 @@ while [ $# -gt 0 ] ; do
       -u)
         if [ -z "$1" ] ; then
             exit_failure_syntax "user argument missing for -u"
+         elif [ -n "$user" ] ; then
+            exit_failure_syntax "only one user can be specified"
         fi
         user="$1"
         shift
@@ -406,6 +410,8 @@ while [ $# -gt 0 ] ; do
       -c)
         if [ -z "$1" ] ; then
             exit_failure_syntax "command argument missing for -c"
+         elif [ -n "$cmd" ] ; then
+            exit_failure_syntax "only one command can be specified"
         fi
         cmd="$1"
         shift