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,""},
 	{}
 };