diff --git a/mvt.cpp b/mvt.cpp
index 16481015..f00a1718 100644
--- a/mvt.cpp
+++ b/mvt.cpp
@@ -15,6 +15,7 @@
 #include "milo/dtoa_milo.h"
 #include "errors.hpp"
 #include "serial.hpp"
+#include "text.hpp"
 
 mvt_geometry::mvt_geometry(int nop, long long nx, long long ny) {
 	this->op = nop;
@@ -592,41 +593,25 @@ std::string mvt_value::toString() const {
 }
 
 void mvt_layer::tag(mvt_feature &feature, std::string const &key, mvt_value const &value) {
-	size_t ko, vo;
-
-	// initialize lazily the first time anyone tags an attribute
-	// to save the time of doing it in decode, which never actually matters.
-	// only tile writers actually need this.
-	if (key_map.size() == 0) {
-		for (size_t i = 0; i < keys.size(); i++) {
-			key_map.emplace(keys[i], i);
-		}
-		for (size_t i = 0; i < values.size(); i++) {
-			value_map.emplace(values[i], i);
-		}
-	}
-
-	std::unordered_map<std::string, size_t>::iterator ki = key_map.find(key);
-	std::unordered_map<mvt_value, size_t>::iterator vi = value_map.find(value);
-
-	if (ki == key_map.end()) {
-		ko = keys.size();
+	size_t key_hash = std::hash<std::string>()(key) % dedup.size();
+	if (dedup[key_hash] >= 0 &&
+	    dedup[key_hash] < (ssize_t) keys.size() &&
+	    keys[dedup[key_hash]] == key) {
+	} else {
+		dedup[key_hash] = keys.size();
 		keys.push_back(key);
-		key_map.emplace(key, ko);
-	} else {
-		ko = ki->second;
 	}
+	feature.tags.push_back(dedup[key_hash]);
 
-	if (vi == value_map.end()) {
-		vo = values.size();
+	size_t value_hash = std::hash<mvt_value>()(value) % dedup.size();
+	if (dedup[value_hash] >= 0 &&
+	    dedup[value_hash] < (ssize_t) values.size() &&
+	    values[dedup[value_hash]] == value) {
+	} else {
+		dedup[value_hash] = values.size();
 		values.push_back(value);
-		value_map.emplace(value, vo);
-	} else {
-		vo = vi->second;
 	}
-
-	feature.tags.push_back(ko);
-	feature.tags.push_back(vo);
+	feature.tags.push_back(dedup[value_hash]);
 }
 
 bool is_integer(const char *s, long long *v) {
diff --git a/mvt.hpp b/mvt.hpp
index ba0d5d57..cc33f7b3 100644
--- a/mvt.hpp
+++ b/mvt.hpp
@@ -174,8 +174,7 @@ struct mvt_layer {
 	void tag(mvt_feature &feature, std::string const &key, mvt_value const &value);
 
 	// For tracking the key-value constants already used in this layer
-	std::unordered_map<std::string, size_t> key_map{};
-	std::unordered_map<mvt_value, size_t> value_map{};
+	std::vector<ssize_t> dedup = std::vector<ssize_t>(65536, -1);
 };
 
 struct mvt_tile {