diff --git a/main.cpp b/main.cpp
index 038495e0..d4738acd 100644
--- a/main.cpp
+++ b/main.cpp
@@ -479,10 +479,10 @@ void do_read_parallel(char *map, long long len, long long initial_offset, const
 	sst.resize(CPUS);
 
 	pthread_t pthreads[CPUS];
-	std::vector<std::set<type_and_string> > file_subkeys;
+	std::vector<std::set<serial_val> > file_subkeys;
 
 	for (size_t i = 0; i < CPUS; i++) {
-		file_subkeys.push_back(std::set<type_and_string>());
+		file_subkeys.push_back(std::set<serial_val>());
 	}
 
 	for (size_t i = 0; i < CPUS; i++) {
diff --git a/mbtiles.cpp b/mbtiles.cpp
index 5af9168c..f56ea043 100644
--- a/mbtiles.cpp
+++ b/mbtiles.cpp
@@ -196,21 +196,21 @@ void mbtiles_erase_zoom(sqlite3 *outdb, int z) {
 	}
 }
 
-bool type_and_string::operator<(const type_and_string &o) const {
-	if (string < o.string) {
+bool serial_val::operator<(const serial_val &o) const {
+	if (s < o.s) {
 		return true;
 	}
-	if (string == o.string && type < o.type) {
+	if (s == o.s && type < o.type) {
 		return true;
 	}
 	return false;
 }
 
-bool type_and_string::operator!=(const type_and_string &o) const {
+bool serial_val::operator!=(const serial_val &o) const {
 	if (type != o.type) {
 		return true;
 	}
-	if (string != o.string) {
+	if (s != o.s) {
 		return true;
 	}
 	return false;
@@ -338,15 +338,15 @@ void tilestats(std::map<std::string, layermap_entry> const &layermap1, size_t el
 					vals++;
 
 					state.nospace = true;
-					state.json_write_stringified(value.string);
+					state.json_write_stringified(value.s);
 				} else {
-					std::string trunc = truncate16(value.string, 256);
+					std::string trunc = truncate16(value.s, 256);
 
-					if (trunc.size() == value.string.size()) {
+					if (trunc.size() == value.s.size()) {
 						vals++;
 
 						state.nospace = true;
-						state.json_write_string(value.string);
+						state.json_write_string(value.s);
 					}
 				}
 			}
@@ -861,7 +861,7 @@ std::map<std::string, layermap_entry> merge_layermaps(std::vector<std::map<std::
 				auto fk2 = out_entry->second.file_keys.find(attribname);
 
 				if (fk2 == out_entry->second.file_keys.end()) {
-					out_entry->second.file_keys.insert(std::pair<std::string, type_and_string_stats>(attribname, fk->second));
+					out_entry->second.file_keys.insert(std::pair<std::string, tilestat>(attribname, fk->second));
 				} else {
 					for (auto val : fk->second.sample_values) {
 						auto pt = std::lower_bound(fk2->second.sample_values.begin(), fk2->second.sample_values.end(), val);
@@ -901,14 +901,14 @@ std::map<std::string, layermap_entry> merge_layermaps(std::vector<std::map<std::
 	return out;
 }
 
-void add_to_file_keys(std::map<std::string, type_and_string_stats> &file_keys, std::string const &attrib, type_and_string const &val) {
+void add_to_file_keys(std::map<std::string, tilestat> &file_keys, std::string const &attrib, serial_val const &val) {
 	if (val.type == mvt_null) {
 		return;
 	}
 
 	auto fka = file_keys.find(attrib);
 	if (fka == file_keys.end()) {
-		file_keys.insert(std::pair<std::string, type_and_string_stats>(attrib, type_and_string_stats()));
+		file_keys.insert(std::pair<std::string, tilestat>(attrib, tilestat()));
 		fka = file_keys.find(attrib);
 	}
 
@@ -918,7 +918,7 @@ void add_to_file_keys(std::map<std::string, type_and_string_stats> &file_keys, s
 	}
 
 	if (val.type == mvt_double) {
-		double d = atof(val.string.c_str());
+		double d = atof(val.s.c_str());
 
 		if (d < fka->second.min) {
 			fka->second.min = d;
diff --git a/mbtiles.hpp b/mbtiles.hpp
index 956b0550..52c19517 100644
--- a/mbtiles.hpp
+++ b/mbtiles.hpp
@@ -9,16 +9,8 @@ extern size_t max_tilestats_attributes;
 extern size_t max_tilestats_sample_values;
 extern size_t max_tilestats_values;
 
-struct type_and_string {
-	int type = 0;
-	std::string string = "";
-
-	bool operator<(const type_and_string &o) const;
-	bool operator!=(const type_and_string &o) const;
-};
-
-struct type_and_string_stats {
-	std::vector<type_and_string> sample_values = std::vector<type_and_string>();  // sorted
+struct tilestat {
+	std::vector<serial_val> sample_values = std::vector<serial_val>();  // sorted
 	double min = INFINITY;
 	double max = -INFINITY;
 	int type = 0;
@@ -26,7 +18,7 @@ struct type_and_string_stats {
 
 struct layermap_entry {
 	size_t id = 0;
-	std::map<std::string, type_and_string_stats> file_keys{};
+	std::map<std::string, tilestat> file_keys{};
 	int minzoom = 0;
 	int maxzoom = 0;
 	std::string description = "";
@@ -84,7 +76,7 @@ void mbtiles_close(sqlite3 *outdb, const char *pgm);
 std::map<std::string, layermap_entry> merge_layermaps(std::vector<std::map<std::string, layermap_entry> > const &maps);
 std::map<std::string, layermap_entry> merge_layermaps(std::vector<std::map<std::string, layermap_entry> > const &maps, bool trunc);
 
-void add_to_file_keys(std::map<std::string, type_and_string_stats> &file_keys, std::string const &layername, type_and_string const &val);
+void add_to_file_keys(std::map<std::string, tilestat> &file_keys, std::string const &layername, serial_val const &val);
 
 unsigned long long fnv1a(std::string const &s);
 
diff --git a/plugin.cpp b/plugin.cpp
index 33407eb9..30ee0fdb 100644
--- a/plugin.cpp
+++ b/plugin.cpp
@@ -274,9 +274,9 @@ std::vector<mvt_layer> parse_layers(int fd, int z, unsigned x, unsigned y, std::
 					mvt_value v = stringified_to_mvt_value(tp, s.c_str());
 					l->second.tag(feature, std::string(properties->value.object.keys[i]->value.string.string), v);
 
-					type_and_string attrib;
+					serial_val attrib;
 					attrib.type = tp;
-					attrib.string = s;
+					attrib.s = s;
 
 					add_to_file_keys(fk->second.file_keys, std::string(properties->value.object.keys[i]->value.string.string), attrib);
 				}
@@ -515,8 +515,8 @@ serial_feature parse_feature(json_pull *jp, int z, unsigned x, unsigned y, std::
 					sf.full_keys.push_back(std::string(properties->value.object.keys[i]->value.string.string));
 					sf.full_values.push_back(v);
 
-					type_and_string attrib;
-					attrib.string = v.s;
+					serial_val attrib;
+					attrib.s = v.s;
 					attrib.type = v.type;
 
 					if (!postfilter) {
diff --git a/serial.cpp b/serial.cpp
index 5a9d7ae5..7317a851 100644
--- a/serial.cpp
+++ b/serial.cpp
@@ -827,12 +827,8 @@ int serialize_feature(struct serialization_state *sst, serial_feature &sf) {
 
 	if (!sst->filters) {
 		for (size_t i = 0; i < sf.full_keys.size(); i++) {
-			type_and_string attrib;
-			attrib.type = sf.full_values[i].type;
-			attrib.string = sf.full_values[i].s;
-
 			auto fk = sst->layermap->find(sf.layername);
-			add_to_file_keys(fk->second.file_keys, sf.full_keys[i], attrib);
+			add_to_file_keys(fk->second.file_keys, sf.full_keys[i], sf.full_values[i]);
 		}
 	}
 
diff --git a/serial.hpp b/serial.hpp
index 9467cd07..05e6d4ea 100644
--- a/serial.hpp
+++ b/serial.hpp
@@ -38,6 +38,9 @@ void deserialize_byte(char **f, signed char *n);
 struct serial_val {
 	int type = 0;
 	std::string s = "";
+
+	bool operator<(const serial_val &o) const;
+	bool operator!=(const serial_val &o) const;
 };
 
 struct serial_feature {
diff --git a/tile-join.cpp b/tile-join.cpp
index 18652271..32ed5a52 100644
--- a/tile-join.cpp
+++ b/tile-join.cpp
@@ -167,7 +167,7 @@ void append_tile(std::string message, int z, unsigned x, unsigned y, std::map<st
 				outfeature.id = feat.id;
 			}
 
-			std::map<std::string, std::pair<mvt_value, type_and_string>> attributes;
+			std::map<std::string, std::pair<mvt_value, serial_val>> attributes;
 			std::vector<std::string> key_order;
 
 			for (size_t t = 0; t + 1 < feat.tags.size(); t += 2) {
@@ -206,11 +206,11 @@ void append_tile(std::string message, int z, unsigned x, unsigned y, std::map<st
 				}
 
 				if (include.count(std::string(key)) || (!exclude_all && exclude.count(std::string(key)) == 0 && exclude_attributes.count(std::string(key)) == 0)) {
-					type_and_string tas;
+					serial_val tas;
 					tas.type = type;
-					tas.string = value;
+					tas.s = value;
 
-					attributes.insert(std::pair<std::string, std::pair<mvt_value, type_and_string>>(key, std::pair<mvt_value, type_and_string>(val, tas)));
+					attributes.insert(std::pair<std::string, std::pair<mvt_value, serial_val>>(key, std::pair<mvt_value, serial_val>(val, tas)));
 					key_order.push_back(key);
 				}
 
@@ -253,14 +253,14 @@ void append_tile(std::string message, int z, unsigned x, unsigned y, std::map<st
 									attributes.erase(fa);
 								}
 
-								type_and_string tas;
+								serial_val tas;
 								tas.type = outval.type;
-								tas.string = joinval;
+								tas.s = joinval;
 
 								// Convert from double to int if the joined attribute is an integer
 								outval = stringified_to_mvt_value(outval.type, joinval.c_str());
 
-								attributes.insert(std::pair<std::string, std::pair<mvt_value, type_and_string>>(joinkey, std::pair<mvt_value, type_and_string>(outval, tas)));
+								attributes.insert(std::pair<std::string, std::pair<mvt_value, serial_val>>(joinkey, std::pair<mvt_value, serial_val>(outval, tas)));
 								key_order.push_back(joinkey);
 							}
 						}
diff --git a/tile.cpp b/tile.cpp
index bdd9df56..5b9f8ef2 100644
--- a/tile.cpp
+++ b/tile.cpp
@@ -1822,11 +1822,7 @@ void add_tilestats(std::string const &layername, int z, std::vector<std::map<std
 		exit(EXIT_IMPOSSIBLE);
 	}
 
-	type_and_string attrib;
-	attrib.type = val.type;
-	attrib.string = val.s;
-
-	add_to_file_keys(fk->second.file_keys, key, attrib);
+	add_to_file_keys(fk->second.file_keys, key, val);
 }
 
 void preserve_attribute(attribute_op op, serial_feature &, char *stringpool, long long *pool_off, std::string &key, serial_val &val, partial &p) {