diff --git a/js/kiri-slice.js b/js/kiri-slice.js
index 5964ae8c..7824f849 100644
--- a/js/kiri-slice.js
+++ b/js/kiri-slice.js
@@ -405,6 +405,9 @@ var gs_kiri_slice = exports;
                     top.traces = last;
                 } else {
                     if (opt.thin) {
+                        var sq2 = Math.sqrt(2),
+                            ons2 = offset1 * sq2,
+                            on2s2 = offsetN * sq2;
                         POLY.expand2(
                             [top.poly],
                             -offset1,
@@ -425,15 +428,22 @@ var gs_kiri_slice = exports;
                             },
                             // thin wall probe
                             function(p1, p2, diff, dist) {
-                                var pall = POLY.nest(POLY.flatten([].appendAll(p1).appendAll(p2)).clone()),
-                                    pnew1 = POLY.expand(pall, -dist, z, null, 1),
-                                    r1 = fillArea(pnew1, 45, offsetN, [], 0, offset1),
-                                    r2 = fillArea(pnew1, 135, offsetN, [], 0, offset1),
-                                    rall = top.thin_fill.appendAll(cullIntersections(r1, r2)),
-                                    pnew2 = POLY.expand(pnew1, -dist, z, null, 1),
-                                    r1 = fillArea(pnew2, 45, offsetN, [], 0, offset1),
-                                    r2 = fillArea(pnew2, 135, offsetN, [], 0, offset1),
-                                    rall = top.thin_fill.appendAll(cullIntersections(r1, r2));
+                                var ds2 = dist * sq2;
+                                if (p2) {
+                                    // nth offset
+                                    var pall = POLY.nest(POLY.flatten([].appendAll(p1).appendAll(p2)).clone()),
+                                        pnew1 = POLY.expand(pall, -dist, z, null, 1),
+                                        r1 = fillArea(pnew1, 45, offsetN, [], ds2, on2s2),
+                                        r2 = fillArea(pnew1, 135, offsetN, [], dist, on2s2),
+                                        rall = top.thin_fill.appendAll(cullIntersections(r1, r2));
+                                } else {
+                                    // first offset
+                                    var pall = POLY.nest(POLY.flatten([].appendAll(p1).appendAll(p2)).clone()),
+                                        pnew1 = POLY.expand(pall, -dist, z, null, 1),
+                                        r1 = fillArea(pnew1, 45, offsetN, [], 0, ons2),
+                                        r2 = fillArea(pnew1, 135, offsetN, [], 0, ons2),
+                                        rall = top.thin_fill.appendAll(cullIntersections(r1, r2));
+                                }
                                 // top.thinner.appendAll(pnew1).appendAll(pnew2);
                             },
                             z);