diff --git a/math.scad b/math.scad
index f8dc707..10938ab 100644
--- a/math.scad
+++ b/math.scad
@@ -438,8 +438,11 @@ function lcm(a,b=[]) =
 //   sum([1,2,3]);  // returns 6.
 //   sum([[1,2,3], [3,4,5], [5,6,7]]);  // returns [9, 12, 15]
 function sum(v, dflt=0) =
+    is_vector(v) ? [for(i=v) 1]*v :
     assert(is_consistent(v), "Input to sum is non-numeric or inconsistent")
-    len(v) == 0 ? dflt : _sum(v,v[0]*0);
+    is_vector(v[0]) ? [for(i=v) 1]*v :
+    len(v) == 0 ? dflt :
+                  _sum(v,v[0]*0);
 
 function _sum(v,_total,_i=0) = _i>=len(v) ? _total : _sum(v,_total+v[_i], _i+1);