diff --git a/source/blender/blenlib/intern/convexhull2d.c b/source/blender/blenlib/intern/convexhull2d.c
index 5669a302bd8..2c29ef042a1 100644
--- a/source/blender/blenlib/intern/convexhull2d.c
+++ b/source/blender/blenlib/intern/convexhull2d.c
@@ -191,6 +191,8 @@ static int pointref_cmp_y(const void *a_, const void *b_)
  * \param  points  An array of 2D points.
  * \param  n  The number of points in points.
  * \param  r_points  An array of the convex hull vertex indices (max is n).
+ *         _must_ be allocated as ``n * 2`` becauise of how its used internally,
+ *         even though the final result will be no more then \a n in size.
  * \returns the number of points in r_points.
  */
 int BLI_convexhull_2d(const float (*points)[2], const int n, int r_points[])
@@ -310,7 +312,7 @@ float BLI_convexhull_aabb_fit_points_2d(const float (*points)[2], unsigned int n
 
 	float angle;
 
-	index_map = MEM_mallocN(sizeof(*index_map) * n, __func__);
+	index_map = MEM_mallocN(sizeof(*index_map) * n * 2, __func__);
 
 	tot = BLI_convexhull_2d((const float (*)[2])points, (int)n, index_map);
 
diff --git a/source/blender/python/mathutils/mathutils_geometry.c b/source/blender/python/mathutils/mathutils_geometry.c
index 8b5b74c480a..584861d4c49 100644
--- a/source/blender/python/mathutils/mathutils_geometry.c
+++ b/source/blender/python/mathutils/mathutils_geometry.c
@@ -1563,7 +1563,7 @@ static PyObject *M_Geometry_convex_hull_2d(PyObject *UNUSED(self), PyObject *poi
 		int *index_map;
 		Py_ssize_t len_ret, i;
 
-		index_map  = MEM_mallocN(sizeof(*index_map) * len, __func__);
+		index_map  = MEM_mallocN(sizeof(*index_map) * len * 2, __func__);
 
 		/* Non Python function */
 		len_ret = BLI_convexhull_2d((const float (*)[2])points, len, index_map);