diff --git a/+quantity/Discrete.m b/+quantity/Discrete.m
index 3de505d4f308ba1c77e63e7499cd787df657a4bc..5a408eef0d863d13e4ccfb471bdc8966ed08636b 100644
--- a/+quantity/Discrete.m
+++ b/+quantity/Discrete.m
@@ -569,7 +569,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 			% alphabetical order.
 						
 			% only sort the grids if there is something to sort
-			if obj(1).nargin > 1
+			if ~isempty(obj) && obj(1).nargin > 1
 				
 				[sortedDomain, I] = obj(1).domain.sort(varargin{:});
 				[obj.domain] = deal(sortedDomain);