diff --git a/plot_transmission_timeline.py b/plot_transmission_timeline.py
index e54d797..a3d1bf3 100755
--- a/plot_transmission_timeline.py
+++ b/plot_transmission_timeline.py
@@ -148,7 +148,7 @@ if __name__ == "__main__":
     print(transmission_df)
 
     # key for columns and level for index
-    transmission_df["goodput"] = transmission_df["payload_size"].groupby(pd.Grouper(level="datetime", freq="{}s".format(args.interval))).sum()
+    transmission_df["goodput"] = transmission_df["payload_size"].groupby(pd.Grouper(level="datetime", freq="{}min".format(args.interval))).sum().dropna()
     print(transmission_df["goodput"])
     exit()