diff --git a/selfdrive/ui/paint.cc b/selfdrive/ui/paint.cc
index fd9a19c468..72dae8134a 100644
--- a/selfdrive/ui/paint.cc
+++ b/selfdrive/ui/paint.cc
@@ -149,7 +149,7 @@ static void ui_draw_line(UIState *s, const vertex_data *v, const int cnt, NVGcol
 static void update_track_data(UIState *s, const cereal::ModelDataV2::XYZTData::Reader &line, track_vertices_data *pvd) {
   const UIScene *scene = &s->scene;
   const float off = 0.5;
-  int max_idx;
+  int max_idx = 0;
   float lead_d;
   if(s->sm->updated("radarState")) {
     lead_d = scene->lead_data[0].getDRel()*2.;