diff --git a/earcut.cpp b/earcut.cpp
index d24eda3a..5f6ba1fd 100644
--- a/earcut.cpp
+++ b/earcut.cpp
@@ -5,6 +5,45 @@ using Coord = long long;
 using N = size_t;
 using Point = std::array<Coord, 2>;
 
+// Return false if the requested adjustment would give
+// any of the polygons that contain vertex N a negative area
+bool can_adjust(drawvec const &dv, std::vector<N> const &indices, size_t n, double *dx, double *dy) {
+	printf("looking for %zu\n", n);
+
+	bool again = true;
+	while (again) {
+		again = false;
+		for (size_t i = 0; i + 2 < indices.size(); i += 3) {
+			for (size_t j = 0; j < 3; j++) {
+				if (indices[i + j] == indices[n]) {
+					drawvec tri;
+					for (size_t k = 0; k < 3; k++) {
+						printf("found %zu %lld,%lld\n", i + j, dv[indices[i + k]].x, dv[indices[i + k]].y);
+
+						tri.push_back(dv[indices[i + k]]);
+						tri[k].op = VT_LINETO;
+
+						if (indices[i + k] == indices[n]) {
+							tri[k].x += *dx;
+							tri[k].y += *dy;
+						}
+					}
+					tri.push_back(tri[0]);
+					tri[0].op = VT_MOVETO;
+					printf("area %f\n", get_area(tri, 0, tri.size()));
+					if (get_area(tri, 0, tri.size()) < 0) {
+						*dx /= 2;
+						*dy /= 2;
+						again = true;
+					}
+				}
+			}
+		}
+	}
+
+	return true;
+}
+
 drawvec fix_by_triangulation(drawvec const &dv, int z, int detail) {
 	std::vector<std::vector<Point>> polygon;
 	drawvec out;
@@ -39,29 +78,37 @@ drawvec fix_by_triangulation(drawvec const &dv, int z, int detail) {
 	while (again) {
 		again = false;
 		for (size_t i = 0; i + 2 < indices.size(); i += 3) {
+			long long cx = 0, cy = 0;
+			for (size_t j = 0; j < 3; j++) {
+				cx += out[indices[i + j]].x;
+				cy += out[indices[i + j]].y;
+			}
+			cx /= 3;
+			cy /= 3;
+
 			for (size_t j = 0; j < 3; j++) {
 				size_t v1 = i + j;
 				size_t v2 = i + ((j + 1) % 3);
 
 				if (std::llround(out[indices[v1]].x / scale) == std::llround(out[indices[v2]].x / scale) &&
 				    std::llround(out[indices[v1]].y / scale) == std::llround(out[indices[v2]].y / scale)) {
-					double ang = atan2(out[indices[v2]].y - out[indices[v1]].y, out[indices[v2]].x - out[indices[v1]].x);
+					double ang = atan2(out[indices[v1]].y - cy, out[indices[v1]].x - cx);
+					double dx = scale * cos(ang) * sqrt(2) * 20;
+					double dy = scale * sin(ang) * sqrt(2) * 20;
+					if (can_adjust(out, indices, v1, &dx, &dy)) {
+						out[indices[v1]].x += dx;
+						out[indices[v1]].y += dy;
+						again = true;
+					}
 
-					printf("at %zu/%zu: %zu and %zu: ", i, j, v1, v2);
-					printf("z%d: was %f,%f to %f,%f ",
-					       z,
-					       out[indices[v1]].x / scale, out[indices[v1]].y / scale,
-					       out[indices[v2]].x / scale, out[indices[v2]].y / scale);
-
-					out[indices[v1]].x -= scale * cos(ang) * sqrt(2);
-					out[indices[v1]].y -= scale * sin(ang) * sqrt(2);
-					out[indices[v2]].x += scale * cos(ang) * sqrt(2);
-					out[indices[v2]].y += scale * sin(ang) * sqrt(2);
-					again = true;
-
-					printf("now %f,%f to %f,%f\n",
-					       out[indices[v1]].x / scale, out[indices[v1]].y / scale,
-					       out[indices[v2]].x / scale, out[indices[v2]].y / scale);
+					ang = atan2(out[indices[v2]].y - cy, out[indices[v2]].x - cx);
+					dx = scale * cos(ang) * sqrt(2) * 20;
+					dy = scale * sin(ang) * sqrt(2) * 20;
+					if (can_adjust(out, indices, v2, &dx, &dy)) {
+						out[indices[v2]].x += dx;
+						out[indices[v2]].y += dy;
+						again = true;
+					}
 				}
 			}
 		}