diff --git a/format_udp_pcap_to_csv.py b/format_udp_pcap_to_csv.py
index 6afe274..769be0c 100755
--- a/format_udp_pcap_to_csv.py
+++ b/format_udp_pcap_to_csv.py
@@ -44,7 +44,8 @@ def format_udp_pcap_to_csv(folder, sender_pcap_name, receiver_pcap_name, output=
         columns={"frame.time_epoch": "arrival_time", "data": "data_hash", "data.len": "data.len_received"}
     )
 
-    transmission_df = sender_df.merge(receiver_df, on="data_hash")
+
+    transmission_df = pd.merge(sender_df, receiver_df, on="data_hash", how="outer")
     transmission_df["delay"] = transmission_df.arrival_time - transmission_df.departure_time
 
     direction = "uplink"