diff --git a/sys/geom/geom_ctl.c b/sys/geom/geom_ctl.c
index 0c0087912693..3eddc832f9b4 100644
--- a/sys/geom/geom_ctl.c
+++ b/sys/geom/geom_ctl.c
@@ -139,7 +139,7 @@ gctl_copyin(struct gctl_req *req)
 	char *p;
 	u_int i;
 
-	if (req->narg > 2048) {
+	if (req->narg > GEOM_CTL_ARG_MAX) {
 		gctl_error(req, "too many arguments");
 		req->arg = NULL;
 		return;
diff --git a/sys/geom/geom_ctl.h b/sys/geom/geom_ctl.h
index b7bec250cc40..50153d019247 100644
--- a/sys/geom/geom_ctl.h
+++ b/sys/geom/geom_ctl.h
@@ -78,7 +78,8 @@ struct gctl_req {
 
 #define GEOM_CTL	_IOW('G', GCTL_VERSION, struct gctl_req)
 
+#define GEOM_CTL_ARG_MAX 2048	/* maximum number of parameters */
+
 #define PATH_GEOM_CTL	"geom.ctl"
 
-
 #endif /* _GEOM_GEOM_CTL_H_ */