diff --git a/geojson.cpp b/geojson.cpp
index c9fc0a8..bb13e55 100644
--- a/geojson.cpp
+++ b/geojson.cpp
@@ -197,6 +197,8 @@ int serialize_geojson_feature(struct serialization_state *sst, json_object *geom
 	sf.feature_minzoom = 0;  // Will be filled in during index merging
 	sf.seq = *(sst->layer_seq);
 
+	checkgeom(sf.geometry, "serialize_geojson_feature");
+
 	if (tippecanoe_layername.size() != 0) {
 		sf.layername = tippecanoe_layername;
 	} else {
diff --git a/geometry.cpp b/geometry.cpp
index f41a983..3afdeff 100644
--- a/geometry.cpp
+++ b/geometry.cpp
@@ -1277,3 +1277,15 @@ drawvec stairstep(drawvec &geom, int z, int detail) {
 
 	return out;
 }
+
+void checkgeom(drawvec const &dv, std::string s) {
+#if 0
+	for (size_t i = 0; i < dv.size(); i++) {
+		if (dv[i].id == 0) {
+			fprintf(stderr, "id lost: %s\n", s.c_str());
+			abort();
+			exit(EXIT_FAILURE);
+		}
+	}
+#endif
+}
diff --git a/geometry.hpp b/geometry.hpp
index 7f01497..0fa9ef4 100644
--- a/geometry.hpp
+++ b/geometry.hpp
@@ -31,6 +31,14 @@ struct draw {
 	      id(0) {
 	}
 
+	draw(int nop, long long nx, long long ny, long long nid)
+	    : x(nx),
+	      op(nop),
+	      y(ny),
+	      necessary(0),
+	      id(nid) {
+	}
+
 	draw()
 	    : x(0),
 	      op(0),
@@ -77,4 +85,7 @@ void check_polygon(drawvec &geom);
 double get_area(drawvec &geom, size_t i, size_t j);
 double get_mp_area(drawvec &geom);
 
+void checkgeom(drawvec const &dv, std::string s);
+
 #endif
+
diff --git a/read_json.cpp b/read_json.cpp
index cdb2211..f5a4754 100644
--- a/read_json.cpp
+++ b/read_json.cpp
@@ -81,7 +81,8 @@ void parse_geometry(int t, json_object *j, drawvec &out, int op, const char *fna
 			}
 
 			draw d(op, x, y);
-			out.push_back(draw(op, x, y));
+			d.id = 12345;
+			out.push_back(d);
 		} else {
 			fprintf(stderr, "%s:%d: malformed point\n", fname, line);
 			json_context(j);
@@ -101,6 +102,8 @@ void parse_geometry(int t, json_object *j, drawvec &out, int op, const char *fna
 
 		out.push_back(draw(VT_CLOSEPATH, 0, 0));
 	}
+
+	checkgeom(out, "parse_geometry");
 }
 
 void canonicalize(json_object *o) {
diff --git a/serial.cpp b/serial.cpp
index 734eb18..134d922 100644
--- a/serial.cpp
+++ b/serial.cpp
@@ -169,6 +169,8 @@ int deserialize_byte_io(FILE *f, signed char *n, long long *geompos) {
 }
 
 static void write_geometry(drawvec const &dv, long long *fpos, FILE *out, const char *fname, long long wx, long long wy) {
+	checkgeom(dv, "write_geometry");
+
 	for (size_t i = 0; i < dv.size(); i++) {
 		if (dv[i].op == VT_MOVETO || dv[i].op == VT_LINETO) {
 			serialize_byte(out, dv[i].op, fpos, fname);
diff --git a/tile.cpp b/tile.cpp
index b4989ff..ee41ea4 100644
--- a/tile.cpp
+++ b/tile.cpp
@@ -292,7 +292,7 @@ void rewrite(drawvec &geom, int z, int nextzoom, int maxzoom, long long *bbox, u
 
 		drawvec geom2;
 		for (size_t i = 0; i < geom.size(); i++) {
-			geom2.push_back(draw(geom[i].op, (geom[i].x + sx) >> geometry_scale, (geom[i].y + sy) >> geometry_scale));
+			geom2.push_back(draw(geom[i].op, (geom[i].x + sx) >> geometry_scale, (geom[i].y + sy) >> geometry_scale, geom[i].id));
 		}
 
 		for (xo = bbox2[0]; xo <= bbox2[2]; xo++) {
@@ -1254,6 +1254,8 @@ bool clip_to_tile(serial_feature &sf, int z, long long buffer) {
 		}
 	}
 
+	checkgeom(sf.geometry, "clip_to_tile1");
+
 	// Can't accept the quick check if guaranteeing no duplication, since the
 	// overlap might have been in the buffer.
 	if (quick != 1 || prevent[P_DUPLICATION]) {
@@ -1273,8 +1275,12 @@ bool clip_to_tile(serial_feature &sf, int z, long long buffer) {
 			clipped = clip_point(sf.geometry, z, buffer);
 		}
 
+		checkgeom(sf.geometry, "clip_to_tile2");
+
 		clipped = remove_noop(clipped, sf.t, 0);
 
+		checkgeom(clipped, "clip_to_tile3");
+
 		// Must clip at z0 even if we don't want clipping, to handle features
 		// that are duplicated across the date line
 
@@ -1304,6 +1310,7 @@ serial_feature next_feature(FILE *geoms, long long *geompos_in, char *metabase,
 		if (sf.t < 0) {
 			return sf;
 		}
+		checkgeom(sf.geometry, "next_feature");
 
 		double progress = floor(((((*geompos_in + *along - alongminus) / (double) todo) + (pass - (2 - passes))) / passes + z) / (maxzoom + 1) * 1000) / 10;
 		if (progress >= *oprogress + 0.1) {
@@ -1746,6 +1753,8 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 				break;
 			}
 
+			checkgeom(sf.geometry, "write_tile");
+
 			if (sf.dropped) {
 				if (find_partial(partials, sf, which_partial, layer_unmaps)) {
 					preserve_attributes(arg->attribute_accum, attribute_accum_state, sf, stringpool, pool_off, partials[which_partial]);