diff --git a/geometry/convex_hull.cpp b/geometry/convex_hull.cpp
index 5a10e96b6ffbeaebf6202eb097addfbd6f692b58..e32b285c836b5914b3eeeb92fea2cbadc7c7778c 100644
--- a/geometry/convex_hull.cpp
+++ b/geometry/convex_hull.cpp
@@ -15,7 +15,7 @@ double cross(dd a, dd b, dd c) {
 
 
 // Find, among v, the points that form a convex hull
-int convex_hull(const vector<dd> &v) {
+int convex_hull(vector<dd> &v) {
   int k = 0;
   vector<int> ans(v.sz * 2);