diff --git a/src/planner/traj_utils/include/traj_utils/polynomial_traj.h b/src/planner/traj_utils/include/traj_utils/polynomial_traj.h
index 72bac9b4..e100bc90 100644
--- a/src/planner/traj_utils/include/traj_utils/polynomial_traj.h
+++ b/src/planner/traj_utils/include/traj_utils/polynomial_traj.h
@@ -234,7 +234,7 @@ class PolynomialTraj
       for (double i = 3; i < order; i += 1)
         for (double j = 3; j < order; j += 1)
         {
-          mat_jerk(i, j) =
+          mat_jerk((size_t)i, (size_t)j) =
               i * (i - 1) * (i - 2) * j * (j - 1) * (j - 2) * pow(ts, i + j - 5) / (i + j - 5);
         }