diff --git a/Makefile b/Makefile
index a39ac0490..82bbe1fc9 100644
--- a/Makefile
+++ b/Makefile
@@ -67,7 +67,7 @@ tippecanoe-enumerate: enumerate.o
 tippecanoe-decode: decode.o projection.o mvt.o write_json.o text.o jsonpull/jsonpull.o dirtiles.o pmtiles_file.o
 	$(CXX) $(PG) $(LIBS) $(FINAL_FLAGS) $(CXXFLAGS) -o $@ $^ $(LDFLAGS) -lm -lz -lsqlite3
 
-tile-join: tile-join.o projection.o mbtiles.o mvt.o memfile.o dirtiles.o jsonpull/jsonpull.o text.o evaluator.o csv.o write_json.o pmtiles_file.o clip.o attribute.o thread.o
+tile-join: tile-join.o projection.o mbtiles.o mvt.o memfile.o dirtiles.o jsonpull/jsonpull.o text.o evaluator.o csv.o write_json.o pmtiles_file.o clip.o attribute.o thread.o read_json.o projection.o
 	$(CXX) $(PG) $(LIBS) $(FINAL_FLAGS) $(CXXFLAGS) -o $@ $^ $(LDFLAGS) -lm -lz -lsqlite3 -lpthread
 
 tippecanoe-json-tool: jsontool.o jsonpull/jsonpull.o csv.o text.o geojson-loop.o
@@ -76,8 +76,8 @@ tippecanoe-json-tool: jsontool.o jsonpull/jsonpull.o csv.o text.o geojson-loop.o
 unit: unit.o text.o sort.o mvt.o
 	$(CXX) $(PG) $(LIBS) $(FINAL_FLAGS) $(CXXFLAGS) -o $@ $^ $(LDFLAGS) -lm -lz -lsqlite3 -lpthread
 
-tippecanoe-overzoom: overzoom.o mvt.o clip.o evaluator.o jsonpull/jsonpull.o text.o attribute.o
-	$(CXX) $(PG) $(LIBS) $(FINAL_FLAGS) $(CXXFLAGS) -o $@ $^ $(LDFLAGS) -lm -lz -lsqlite3 -lpthread
+tippecanoe-overzoom: overzoom.o mvt.o clip.o evaluator.o jsonpull/jsonpull.o text.o attribute.o read_json.o
+	$(CXX) $(PG) $(LIBS) $(FINAL_FLAGS) $(CXXFLAGS) -o $@ $^ $(LDFLAGS) -lm -lz -lsqlite3 -lpthread projection.o
 
 -include $(wildcard *.d)
 
diff --git a/clip.cpp b/clip.cpp
index a220e2ad6..4bd570200 100644
--- a/clip.cpp
+++ b/clip.cpp
@@ -10,6 +10,7 @@
 #include "evaluator.hpp"
 #include "serial.hpp"
 #include "attribute.hpp"
+#include "read_json.hpp"
 
 static std::vector<std::pair<double, double>> clip_poly1(std::vector<std::pair<double, double>> &geom,
 							 long long minx, long long miny, long long maxx, long long maxy,
@@ -886,7 +887,11 @@ Joined values win over original values, at least for the moment.
 
 */
 
-void join_by_id(mvt_feature &feature, const json_object *j) {
+void join_by_id(mvt_layer &layer, mvt_feature &feature, const json_object *j, std::shared_ptr<std::string> tile_stringpool) {
+	if (!feature.has_id) {
+		return;
+	}
+
 	if (j->type != JSON_HASH) {
 		fprintf(stderr, "list of attributes to be joined to features is not a json object\n");
 		exit(EXIT_JSON);
@@ -894,17 +899,47 @@ void join_by_id(mvt_feature &feature, const json_object *j) {
 
 	for (size_t i = 0; i < j->value.object.length; i++) {
 		const json_object *key = j->value.object.keys[i];
+		if (key->type == JSON_STRING) {
+			unsigned long long feature_id = atoll(j->value.object.keys[i]->value.string.string);
+			if (feature_id == feature.id) {
+				const json_object *value = j->value.object.values[i];
+
+				if (value->type == JSON_HASH) {
+					for (size_t a = 0; a < value->value.object.length; a++) {
+						json_object *k = value->value.object.keys[a];
+						json_object *v = value->value.object.values[a];
+
+						if (k->type != JSON_STRING) {
+							fprintf(stderr, "Expected string for key in json join, not %s\n", json_stringify(k));
+							exit(EXIT_JSON);
+						}
+
+						serial_val sv = stringify_value(v, "joined json", 1, value);
+						mvt_value mv = stringified_to_mvt_value(sv.type, sv.s.c_str(), tile_stringpool);
+						layer.tag(feature, k->value.string.string, mv);
+					}
+				} else {
+					fprintf(stderr, "Expected attribute object for value in json join, not %s\n", json_stringify(value));
+					exit(EXIT_JSON);
+				}
+
+				break;
+			}
+		} else {
+			fprintf(stderr, "Expected string for key in json join, not %s\n", json_stringify(key));
+			exit(EXIT_JSON);
+		}
 	}
 }
 
-std::string overzoom(const mvt_tile &tile, int oz, int ox, int oy, int nz, int nx, int ny,
+std::string overzoom(mvt_tile tile, int oz, int ox, int oy, int nz, int nx, int ny,
 		     int detail, int buffer, std::set<std::string> const &keep, bool do_compress,
 		     std::vector<std::pair<unsigned, unsigned>> *next_overzoomed_tiles,
 		     bool demultiply, json_object *filter, bool preserve_input_order, std::unordered_map<std::string, attribute_op> const &attribute_accum, std::vector<std::string> const &unidecode_data, json_object *join_attributes_json) {
 	mvt_tile outtile;
 	std::shared_ptr<std::string> tile_stringpool = std::make_shared<std::string>();
 
-	for (auto const &layer : tile.layers) {
+	for (auto &layer : tile.layers) {
 		mvt_layer outlayer = mvt_layer();
 
 		int det = detail;
@@ -923,7 +958,7 @@ std::string overzoom(const mvt_tile &tile, int oz, int ox, int oy, int nz, int n
 
 		for (auto feature : layer.features) {
 			if (join_attributes_json != NULL) {
-				join_by_id(feature, join_attributes_json);
+				join_by_id(layer, feature, join_attributes_json, tile_stringpool);
 			}
 
 			bool flush_multiplier_cluster = false;
diff --git a/geometry.hpp b/geometry.hpp
index 5d4ea1d7c..4d72cad54 100644
--- a/geometry.hpp
+++ b/geometry.hpp
@@ -100,7 +100,7 @@ void visvalingam(drawvec &ls, size_t start, size_t end, double threshold, size_t
 int pnpoly(const drawvec &vert, size_t start, size_t nvert, long long testx, long long testy);
 double distance_from_line(long long point_x, long long point_y, long long segA_x, long long segA_y, long long segB_x, long long segB_y);
 
-std::string overzoom(const mvt_tile &tile, int oz, int ox, int oy, int nz, int nx, int ny,
+std::string overzoom(mvt_tile tile, int oz, int ox, int oy, int nz, int nx, int ny,
 		     int detail, int buffer, std::set<std::string> const &keep, bool do_compress,
 		     std::vector<std::pair<unsigned, unsigned>> *next_overzoomed_tiles,
 		     bool demultiply, json_object *filter, bool preserve_input_order,
diff --git a/jsonpull/jsonpull.c b/jsonpull/jsonpull.c
index 04ca0f296..01ee5d8ca 100644
--- a/jsonpull/jsonpull.c
+++ b/jsonpull/jsonpull.c
@@ -905,7 +905,7 @@ void json_disconnect(json_object *o) {
 	o->parent = NULL;
 }
 
-static void json_print_one(struct string *val, json_object *o) {
+static void json_print_one(struct string *val, const json_object *o) {
 	if (o == NULL) {
 		string_append_string(val, "...");
 	} else if (o->type == JSON_STRING) {
@@ -955,7 +955,7 @@ static void json_print_one(struct string *val, json_object *o) {
 	}
 }
 
-static void json_print(struct string *val, json_object *o) {
+static void json_print(struct string *val, const json_object *o) {
 	if (o == NULL) {
 		// Hash value in incompletely read hash
 		string_append_string(val, "...");
@@ -987,7 +987,7 @@ static void json_print(struct string *val, json_object *o) {
 	}
 }
 
-char *json_stringify(json_object *o) {
+char *json_stringify(const json_object *o) {
 	struct string val;
 	string_init(&val);
 	json_print(&val, o);
diff --git a/jsonpull/jsonpull.h b/jsonpull/jsonpull.h
index b19e0e8e9..40ae28b15 100644
--- a/jsonpull/jsonpull.h
+++ b/jsonpull/jsonpull.h
@@ -89,7 +89,7 @@ void json_disconnect(json_object *j);
 
 json_object *json_hash_get(json_object *o, const char *s);
 
-char *json_stringify(json_object *o);
+char *json_stringify(const json_object *o);
 
 #ifdef __cplusplus
 }
diff --git a/read_json.cpp b/read_json.cpp
index 45e136582..2b1f3f3bf 100644
--- a/read_json.cpp
+++ b/read_json.cpp
@@ -42,7 +42,7 @@ int mb_geometry[GEOM_TYPES] = {
 	VT_POLYGON,
 };
 
-void json_context(json_object *j) {
+void json_context(const json_object *j) {
 	char *s = json_stringify(j);
 
 	if (strlen(s) >= 500) {
@@ -121,7 +121,7 @@ void parse_geometry(int t, json_object *j, drawvec &out, int op, const char *fna
 // type and stringified value. All numeric values, even if they are integers,
 // even integers that are too large to fit in a double but will still be
 // stringified with their original precision, are recorded here as mvt_double.
-serial_val stringify_value(json_object *value, const char *reading, int line, json_object *feature) {
+serial_val stringify_value(json_object const *value, char const *reading, int line, json_object const *feature) {
 	serial_val sv;
 
 	if (value != NULL) {
diff --git a/read_json.hpp b/read_json.hpp
index 1d9374abd..5a16b40a8 100644
--- a/read_json.hpp
+++ b/read_json.hpp
@@ -10,7 +10,6 @@ extern const char *geometry_names[GEOM_TYPES];
 extern int geometry_within[GEOM_TYPES];
 extern int mb_geometry[GEOM_TYPES];
 
-void json_context(json_object *j);
+void json_context(const json_object *j);
 void parse_geometry(int t, json_object *j, drawvec &out, int op, const char *fname, int line, json_object *feature);
-
-serial_val stringify_value(json_object *value, const char *reading, int line, json_object *feature);
+serial_val stringify_value(json_object const *, char const *, int, json_object const *);