diff --git a/clip.cpp b/clip.cpp
index 33e16722..28ec0aca 100644
--- a/clip.cpp
+++ b/clip.cpp
@@ -895,13 +895,13 @@ static drawvec simplify_lines_basic(drawvec &geom, int z, int detail, double sim
 
 	for (size_t i = 0; i < geom.size(); i++) {
 		if (geom[i].op == VT_MOVETO) {
-			geom[i].necessary = 1;
+			geom[i].necessary = 127;
 		} else if (geom[i].op == VT_LINETO) {
 			geom[i].necessary = 0;
 			// if this is actually the endpoint, not an intermediate point,
 			// it will be marked as necessary below
 		} else {
-			geom[i].necessary = 1;
+			geom[i].necessary = 127;
 		}
 	}
 
@@ -914,8 +914,8 @@ static drawvec simplify_lines_basic(drawvec &geom, int z, int detail, double sim
 				}
 			}
 
-			geom[i].necessary = 1;
-			geom[j - 1].necessary = 1;
+			geom[i].necessary = 127;
+			geom[j - 1].necessary = 127;
 
 			if (j - i > 1) {
 				douglas_peucker(geom, i, j - i, res * simplification, 2, retain, false);
diff --git a/geometry.cpp b/geometry.cpp
index 30f8fd9e..59aa30aa 100644
--- a/geometry.cpp
+++ b/geometry.cpp
@@ -40,9 +40,11 @@ drawvec decode_geometry(const char **meta, int z, unsigned tx, unsigned ty, long
 
 		if (d.op == VT_MOVETO || d.op == VT_LINETO) {
 			long long dx, dy;
+			signed char necessary;
 
 			deserialize_long_long(meta, &dx);
 			deserialize_long_long(meta, &dy);
+			deserialize_byte(meta, &necessary);
 
 			wx += dx * (1 << geometry_scale);
 			wy += dy * (1 << geometry_scale);
@@ -62,6 +64,7 @@ drawvec decode_geometry(const char **meta, int z, unsigned tx, unsigned ty, long
 
 			d.x = wwx;
 			d.y = wwy;
+			d.necessary = necessary;
 		}
 
 		out.push_back(d);
@@ -224,11 +227,11 @@ drawvec impose_tile_boundaries(const drawvec &geom, long long extent) {
 			if (c > 1) {  // clipped
 				if (x1 != geom[i - 1].x || y1 != geom[i - 1].y) {
 					out.emplace_back(VT_LINETO, x1, y1);
-					out[out.size() - 1].necessary = 1;
+					out[out.size() - 1].necessary = 127;
 				}
 				if (x2 != geom[i - 0].x || y2 != geom[i - 0].y) {
 					out.emplace_back(VT_LINETO, x2, y2);
-					out[out.size() - 1].necessary = 1;
+					out[out.size() - 1].necessary = 127;
 				}
 			}
 		}
@@ -245,13 +248,13 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 
 	for (size_t i = 0; i < geom.size(); i++) {
 		if (geom[i].op == VT_MOVETO) {
-			geom[i].necessary = 1;
+			geom[i].necessary = 127;
 		} else if (geom[i].op == VT_LINETO) {
 			geom[i].necessary = 0;
 			// if this is actually the endpoint, not an intermediate point,
 			// it will be marked as necessary below
 		} else {
-			geom[i].necessary = 1;
+			geom[i].necessary = 127;
 		}
 
 		if (prevent[P_SIMPLIFY_SHARED_NODES]) {
@@ -265,7 +268,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 
 			auto pt = std::lower_bound(shared_nodes.begin(), shared_nodes.end(), geom[i]);
 			if (pt != shared_nodes.end() && *pt == geom[i]) {
-				geom[i].necessary = true;
+				geom[i].necessary = 127;
 			}
 
 			if (nodepos > 0) {
@@ -281,7 +284,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 				n.index = encode_quadkey((unsigned) d.x, (unsigned) d.y);
 
 				if (bsearch(&n, shared_nodes_map, nodepos / sizeof(node), sizeof(node), nodecmp) != NULL) {
-					geom[i].necessary = true;
+					geom[i].necessary = 127;
 				}
 			}
 		}
@@ -300,8 +303,8 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 				}
 			}
 
-			geom[i].necessary = 1;
-			geom[j - 1].necessary = 1;
+			geom[i].necessary = 127;
+			geom[j - 1].necessary = 127;
 
 			// empirical mapping from douglas-peucker simplifications
 			// to visvalingam simplifications that yield similar
diff --git a/geometry.hpp b/geometry.hpp
index 997842c7..fad6f339 100644
--- a/geometry.hpp
+++ b/geometry.hpp
@@ -27,20 +27,24 @@ struct draw {
 	long long x : 40;
 	signed char op;
 	long long y : 40;
+
+	// 0:       not necessary
+	// 127:     always necessary
+	// other n: necessary at detail n/4
 	signed char necessary;
 
 	draw(int nop, long long nx, long long ny)
 	    : x(nx),
 	      op(nop),
 	      y(ny),
-	      necessary(0) {
+	      necessary(127) {
 	}
 
 	draw()
 	    : x(0),
 	      op(0),
 	      y(0),
-	      necessary(0) {
+	      necessary(127) {
 	}
 
 	bool operator<(draw const &s) const {
diff --git a/serial.cpp b/serial.cpp
index bd694ebb..6df96758 100644
--- a/serial.cpp
+++ b/serial.cpp
@@ -160,6 +160,7 @@ static void write_geometry(drawvec const &dv, std::string &out, long long wx, lo
 			serialize_byte(out, dv[i].op);
 			serialize_long_long(out, dv[i].x - wx);
 			serialize_long_long(out, dv[i].y - wy);
+			serialize_byte(out, dv[i].necessary);
 			wx = dv[i].x;
 			wy = dv[i].y;
 		} else {