diff --git a/plot_single_transmission_timeline.py b/plot_single_transmission_timeline.py
index 69db340..97f89b4 100755
--- a/plot_single_transmission_timeline.py
+++ b/plot_single_transmission_timeline.py
@@ -79,6 +79,7 @@ if __name__ == "__main__":
         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)
+        serial_df.sort_index()
 
         transmission_df = pd.merge_asof(
             transmission_df,
diff --git a/plot_transmission_timeline.py b/plot_transmission_timeline.py
index ea7c45e..bd822d7 100755
--- a/plot_transmission_timeline.py
+++ b/plot_transmission_timeline.py
@@ -165,6 +165,7 @@ if __name__ == "__main__":
     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)
+    serial_df.sort_index()
 
     transmission_df = pd.merge_asof(
         transmission_df,