diff --git a/tile.cc b/tile.cc
index 6716294e..9be0285d 100644
--- a/tile.cc
+++ b/tile.cc
@@ -340,7 +340,7 @@ void douglas_peucker(struct draw *geom, int n, double e) {
 }
 
 int simplify_lines(struct draw *geom, int n, int z, int detail) {
-	int res = 1 << (32 - detail - z);
+	int res = 1 << (32 - detail - z + 2);
 
 	int i;
 	for (i = 0; i < n; i++) {