diff --git a/plot_single_transmission_EM9190.py b/plot_single_transmission_EM9190.py
index 4517fb3..b6f78a7 100755
--- a/plot_single_transmission_EM9190.py
+++ b/plot_single_transmission_EM9190.py
@@ -90,7 +90,7 @@ if __name__ == "__main__":
         #transmission_df = transmission_df.filter(["goodput", "datetime", "ack_rtt", "goodput_rolling", "snd_cwnd"])
 
         # read serial csv
-        serial_df = pd.read_csv(args.serial_file)
+        serial_df = pd.read_csv(args.serial_file, dtype=dict(Cell_ID=str),)
         serial_df["datetime"] = pd.to_datetime(serial_df["datetime"]) - pd.Timedelta(hours=1)
         serial_df = serial_df.set_index("datetime")
         serial_df.index = pd.to_datetime(serial_df.index)