Index: head/sys/geom/geom_ctl.c
===================================================================
--- head/sys/geom/geom_ctl.c
+++ head/sys/geom/geom_ctl.c
@@ -396,12 +396,15 @@
 	struct g_class *cp;
 
 	p = gctl_get_asciiparam(req, arg);
-	if (p == NULL)
+	if (p == NULL) {
+		gctl_error(req, "Missing %s argument", arg);
 		return (NULL);
+	}
 	LIST_FOREACH(cp, &g_classes, class) {
 		if (!strcmp(p, cp->name))
 			return (cp);
 	}
+	gctl_error(req, "Class not found: \"%s\"", p);
 	return (NULL);
 }
 
@@ -413,8 +416,10 @@
 	struct g_geom *gp;
 
 	p = gctl_get_asciiparam(req, arg);
-	if (p == NULL)
+	if (p == NULL) {
+		gctl_error(req, "Missing %s argument", arg);
 		return (NULL);
+	}
 	LIST_FOREACH(mp, &g_classes, class) {
 		if (mpr != NULL && mpr != mp)
 			continue;
@@ -434,8 +439,10 @@
 	struct g_provider *pp;
 
 	p = gctl_get_asciiparam(req, arg);
-	if (p == NULL)
+	if (p == NULL) {
+		gctl_error(req, "Missing '%s' argument", arg);
 		return (NULL);
+	}
 	pp = g_provider_by_name(p);
 	if (pp != NULL)
 		return (pp);
@@ -453,10 +460,8 @@
 	g_topology_assert();
 	req = arg;
 	mp = gctl_get_class(req, "class");
-	if (mp == NULL) {
-		gctl_error(req, "Class not found");
+	if (mp == NULL)
 		return;
-	}
 	if (mp->ctlreq == NULL) {
 		gctl_error(req, "Class takes no requests");
 		return;