diff --git a/src/handler.c b/src/handler.c
index fe0435b..719fc4c 100644
--- a/src/handler.c
+++ b/src/handler.c
@@ -1,68 +1,70 @@
 /* 
  * Copyright (C) 2014 Philipp Marek <philipp.marek@linbit.com>
  * 
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  * 
  * This software is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  * 
  * You should have received a copy of the GNU General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
 #include <stdlib.h>
 #include <string.h>
 #include <errno.h>
 #include <arpa/inet.h>
 #include <inttypes.h>
 #include <stdio.h>
 #include <assert.h>
 #include <time.h>
 #include "ticket.h"
 #include "config.h"
 #include "inline-fn.h"
 #include "log.h"
 #include "pacemaker.h"
 #include "booth.h"
 #include "handler.h"
 
 
 
 /** Runs an external handler.
  * See eg. 'before-acquire-handler'.
  * TODO: timeout, async operation?. */
 int run_handler(struct ticket_config *tk,
 		const char *cmd, int synchronous)
 {
 	int rv;
 	char expires[16];
 
+	if (!cmd)
+		return 0;
 
 	assert(synchronous);
 	sprintf(expires, "%" PRId64, tk->term_expires);
 
 	rv = setenv("BOOTH_TICKET", tk->name, 1) ||
 		setenv("BOOTH_LOCAL", local->addr_string, 1) ||
 		setenv("BOOTH_CONF_NAME", booth_conf->name, 1) ||
 		setenv("BOOTH_CONF_PATH", cl.configfile, 1) ||
 		setenv("BOOTH_TICKET_EXPIRES", expires, 1);
 
 	if (rv) {
 		log_error("Cannot set environment: %d", errno);
 	} else {
 		rv = system(cmd);
 		if (rv)
 			log_error("Error calling \"%s\": %s",
 					cmd, interpret_rv(rv));
 		else
 			log_info("Ran \"%s\" successfully.", cmd);
 	}
 
 	return rv;
 }