diff --git a/slmodemd/modem_cmdline.c b/slmodemd/modem_cmdline.c
index 9f80619..ec20a91 100644
--- a/slmodemd/modem_cmdline.c
+++ b/slmodemd/modem_cmdline.c
@@ -125,7 +125,7 @@ static struct opt {
 	{'s',"shortbuffer","use short buffer (4 periods length)"},
 	{'d',"debug","debug level (developers only, for ./sl...)",OPTIONAL,INTEGER,"0"},
 	{'l',"log","logging mode",OPTIONAL,INTEGER,"5"},
-	{'e',"exec","path to external application that transmits audio over the socket (required)"},
+	{'e',"exec","path to external application that transmits audio over the socket (required)",MANDATORY,STRING,""},
 	{}
 };
 
diff --git a/slmodemd/modem_main.c b/slmodemd/modem_main.c
index 998090a..2a95097 100644
--- a/slmodemd/modem_main.c
+++ b/slmodemd/modem_main.c
@@ -635,7 +635,12 @@ static int socket_start (struct modem *m)
 		char str[16];
 		snprintf(str,sizeof(str),"%d",sockets[0]);
 		close(sockets[1]);
-		execl(modem_exec,modem_exec,m->dial_string,str,NULL);
+		ret = execl(modem_exec,modem_exec,m->dial_string,str,NULL);
+		if (ret == -1) {
+			ERR("prog: %s\n", modem_exec);
+			perror("execl");
+			exit(-1);
+		}
 	} else {
 		close(sockets[0]);
 		dev->fd = sockets[1];