diff --git a/modules/prediction/predictor/predictor.cc b/modules/prediction/predictor/predictor.cc
index 64ffe5438f6c2db45102f6cc827d58a60e935ccb..110c861d40b27f4e7c4ded3f8c139b8a19f80c17 100644
--- a/modules/prediction/predictor/predictor.cc
+++ b/modules/prediction/predictor/predictor.cc
@@ -41,7 +41,7 @@ void Predictor::GenerateTrajectory(
 
 void Predictor::SetEqualProbability(double probability, int start_index) {
   int num = GetTrajectorySize();
-  if (start_index > 0 && num > 0 && num > start_index) {
+  if (start_index >= 0 && num > 0 && num > start_index) {
     probability = probability / (double(num - start_index));
     for (int i = start_index; i < num; ++i) {
       prediction_obstacle_.mutable_trajectory(i)->set_probability(probability);
diff --git a/modules/prediction/predictor/vehicle/free_move_predictor.cc b/modules/prediction/predictor/vehicle/free_move_predictor.cc
index 1e217142133c6916ae526057215fe730e8d7c781..379001b8a616ae3185b09cf0b4597f1ed174192c 100644
--- a/modules/prediction/predictor/vehicle/free_move_predictor.cc
+++ b/modules/prediction/predictor/vehicle/free_move_predictor.cc
@@ -50,14 +50,15 @@ void FreeMovePredictor::Predict(Obstacle* obstacle) {
 
   std::vector<TrajectoryPoint> points(0);
   double total_time = FLAGS_prediction_duration;
-  // TODO(jinghao):
+  // TODO(kechxu):
   // draw_free_move_trajectory(position, velocity, obstacle->kf_motion_tracker(),
   //                           total_time, points);
   Trajectory trajectory;
   GenerateTrajectory(points, &trajectory);
-  trajectory.set_probability(1.0);
+  int start_index = 0;
   prediction_obstacle_.set_predicted_period(total_time);
   prediction_obstacle_.add_trajectory()->CopyFrom(trajectory);
+  SetEqualProbability(1.0, start_index);
 }
 
 }  // prediction