diff --git a/forest/bonsai/simulate_gps_data.py b/forest/bonsai/simulate_gps_data.py
index 3d317ca9..6031d334 100644
--- a/forest/bonsai/simulate_gps_data.py
+++ b/forest/bonsai/simulate_gps_data.py
@@ -1394,7 +1394,10 @@ def sim_gps_data(
         obs = remove_data(all_traj, cycle, percentage, no_of_days)
         obs_pd = prepare_data(obs, int(timestamp_s / 1000), tz_str)
         obs_pd['user'] = user + 1
-        gps_data = pd.concat([gps_data, obs_pd])
+        if gps_data.empty:
+            gps_data = obs_pd
+        else:
+            gps_data = pd.concat([gps_data, obs_pd])
 
         user += 1
         ind += 1