diff --git a/pool.c b/pool.c
index cc55df9..4641afc 100644
--- a/pool.c
+++ b/pool.c
@@ -14,7 +14,7 @@ static int hash(const char *s) {
 	return h;
 }
 
-struct pool_val *pool(struct pool *p, char *s, int type) {
+struct pool_val *pool(struct pool *p, const char *s, int type) {
 	int h = hash(s);
 	struct pool_val **v = &(p->vals[h]);
 
@@ -83,7 +83,7 @@ int is_pooled(struct pool *p, const char *s, int type) {
 void pool_free1(struct pool *p, void (*func)(void *)) {
 	while (p->head != NULL) {
 		if (func != NULL) {
-			func(p->head->s);
+			func((void *) p->head->s);
 		}
 
 		struct pool_val *next = p->head->next;
diff --git a/pool.h b/pool.h
index 683b551..100dd76 100644
--- a/pool.h
+++ b/pool.h
@@ -1,5 +1,5 @@
 struct pool_val {
-	char *s;
+	const char *s;
 	int type;
 	int n;
 
@@ -17,7 +17,7 @@ struct pool {
 	int n;
 };
 
-struct pool_val *pool(struct pool *p, char *s, int type);
+struct pool_val *pool(struct pool *p, const char *s, int type);
 void pool_free(struct pool *p);
 void pool_free_strings(struct pool *p);
 void pool_init(struct pool *p, int n);
diff --git a/tile-join.cc b/tile-join.cc
index af02b0d..89f9e8c 100644
--- a/tile-join.cc
+++ b/tile-join.cc
@@ -100,6 +100,10 @@ void handle(std::string message, int z, unsigned x, unsigned y, struct pool **fi
 			*nlayers = ll + 1;
 		}
 
+		struct pool keys, values;
+		pool_init(&keys, 0);
+		pool_init(&values, 0);
+
 		for (int f = 0; f < layer.features_size(); f++) {
 			mapnik::vector::tile_feature feat = layer.features(f);
 			mapnik::vector::tile_feature *outfeature = outlayer->add_features();
@@ -150,10 +154,30 @@ void handle(std::string message, int z, unsigned x, unsigned y, struct pool **fi
 					pool(file_keys[ll], strdup(key), type);
 				}
 
-				printf("%d: %s=%s\n", type, key, value);
+				struct pool_val *k, *v;
+
+				if (is_pooled(&keys, key, VT_STRING)) {
+					k = pool(&keys, key, VT_STRING);
+				} else {
+					k = pool(&keys, strdup(key), VT_STRING);
+				}
+
+				if (is_pooled(&values, value, type)) {
+					v = pool(&values, value, type);
+				} else {
+					v = pool(&values, strdup(value), type);
+				}
+
+				outfeature->add_tags(k->n);
+				outfeature->add_tags(v->n);
+
+				printf("%d: %s=%s  %d=%d\n", type, key, value, k->n, v->n);
 				free(value);
 			}
 		}
+
+		pool_free_strings(&keys);
+		pool_free_strings(&values);
 	}
 }