diff --git a/src/skin/toks_skin_default.c b/src/skin/toks_skin_default.c
index a0cdbe7..a759589 100644
--- a/src/skin/toks_skin_default.c
+++ b/src/skin/toks_skin_default.c
@@ -20,7 +20,8 @@ const struct argv_option toks_default_options[] = {
 				"in all other cases."},
 
 	{"uuid",		'u',TAG_UUID,ARGV_OPTARG_REQUIRED,0,0,"<uuid>",
-				"set the service identifier to %s."},
+				"set the service identifier to %s, which needs "
+				"to be in the format {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}."},
 
 	{"refstr",		'f',TAG_REFSTR,ARGV_OPTARG_REQUIRED,0,0,"<refstr>",
 				"include the reference string %s in log records"