diff --git a/math.scad b/math.scad
index 79d5ffa..720d0e6 100644
--- a/math.scad
+++ b/math.scad
@@ -585,7 +585,7 @@ function lcm(a,b=[]) =
 function sum(v, dflt=0) =
     v==[]? dflt :
     assert(is_consistent(v), "Input to sum is non-numeric or inconsistent")
-    is_vector(v) ? [for(i=[1:len(v)]) 1]*v :
+    is_vector(v) || is_matrix(v) ? [for(i=[1:len(v)]) 1]*v :
     _sum(v,v[0]*0);
 
 function _sum(v,_total,_i=0) = _i>=len(v) ? _total : _sum(v,_total+v[_i], _i+1);