diff --git a/shapes.scad b/shapes.scad
index f0984fe..f485b5a 100644
--- a/shapes.scad
+++ b/shapes.scad
@@ -174,6 +174,7 @@ module cuboid(
                         }
                     }
                 } else if (chamfer<0) {
+                    assert(edges == EDGES_ALL || edges[2] == [0,0,0,0], "Cannot use negative chamfer with Z aligned edges.");
                     ach = abs(chamfer);
                     cube(size, center=true);
 
@@ -260,6 +261,7 @@ module cuboid(
                         }
                     }
                 } else if (rounding<0) {
+                    assert(edges == EDGES_ALL || edges[2] == [0,0,0,0], "Cannot use negative rounding with Z aligned edges.");
                     ard = abs(rounding);
                     cube(size, center=true);
 
@@ -322,6 +324,7 @@ module cuboid(
     }
 }
 
+
 function cuboid(
     size=[1,1,1],
     p1, p2,