diff --git a/geojson.c b/geojson.c
index bc2a11f0..eb485415 100644
--- a/geojson.c
+++ b/geojson.c
@@ -129,11 +129,11 @@ int indexcmp(const void *v1, const void *v2) {
 	}
 }
 
-struct pool_val *pool(struct pool *p, char *s, int type) {
+struct pool_val *pool1(struct pool *p, char *s, int type, int (*compare)(const char *, const char *)) {
 	struct pool_val **v = &(p->vals);
 
 	while (*v != NULL) {
-		int cmp = strcmp(s, (*v)->s);
+		int cmp = compare(s, (*v)->s);
 
 		if (cmp == 0) {
 			cmp = type - (*v)->type;
@@ -167,6 +167,27 @@ struct pool_val *pool(struct pool *p, char *s, int type) {
 	return *v;
 }
 
+struct pool_val *pool(struct pool *p, char *s, int type) {
+	return pool1(p, s, type, strcmp);
+}
+
+int llcmp(const char *v1, const char *v2) {
+	long long *ll1 = (long long *) v1;
+	long long *ll2 = (long long *) v2;
+
+	if (*ll1 < *ll2) {
+		return -1;
+	} else if (*ll1 > *ll2) {
+		return 1;
+	} else {
+		return 0;
+	}
+}
+
+struct pool_val *pool_long_long(struct pool *p, long long *s, int type) {
+	return pool1(p, (char *) s, type, llcmp);
+}
+
 void pool_free(struct pool *p) {
 	while (p->head != NULL) {
 		struct pool_val *next = p->head->next;
diff --git a/tile.cc b/tile.cc
index 5f6656f2..dbf59381 100644
--- a/tile.cc
+++ b/tile.cc
@@ -145,6 +145,12 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 	values.head = NULL;
 	values.tail = NULL;
 
+	struct pool dup;
+	dup.n = 1;
+	dup.vals = NULL;
+	dup.head = NULL;
+	dup.tail = NULL;
+
 	double interval = 1;
 	double seq = 0;
 
@@ -170,6 +176,12 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 		}
 
 		if (t == VT_POINT || draw(&meta, NULL, z, tx, ty, detail)) {
+			struct pool_val *pv = pool_long_long(&dup, &i->fpos, 0);
+			if (pv->n == 0) {
+				continue;
+			}
+			pv->n = 0;
+
 			meta = metabase + i->fpos;
 			deserialize_int(&meta, &t);
 
@@ -220,6 +232,8 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 		}
 	}
 	pool_free(&keys);
+	pool_free(&values);
+	pool_free(&dup);
 
 	std::string s;
 	std::string compressed;
diff --git a/tile.h b/tile.h
index 8ff23d5d..a9d7714b 100644
--- a/tile.h
+++ b/tile.h
@@ -37,6 +37,7 @@ struct pool {
 void deserialize_int(char **f, int *n);
 struct pool_val *deserialize_string(char **f, struct pool *p, int type);
 struct pool_val *pool(struct pool *p, char *s, int type);
+struct pool_val *pool_long_long(struct pool *p, long long *val, int type);
 void pool_free(struct pool *p);