diff --git a/plot_transmission_timeline.py b/plot_transmission_timeline.py
index f13ea92..43a83da 100755
--- a/plot_transmission_timeline.py
+++ b/plot_transmission_timeline.py
@@ -189,9 +189,11 @@ if __name__ == "__main__":
 
     host = host_subplot(111, axes_class=axisartist.Axes)
 
+    transmission_df["index"] = transmission_df.index
+
     cmap = matplotlib.cm.get_cmap("Set3")
     for c in transmission_df["cellID"].unique():
-        bounds = transmission_df[[transmission_df.index, "cellID"]].groupby("cellID").agg(["min", "max"]).loc[c]
+        bounds = transmission_df[["index", "cellID"]].groupby("cellID").agg(["min", "max"]).loc[c]
         host.axvspan(bounds.min(), bounds.max() + 1, alpha=0.3, color=cmap.colors[c])
 
     plt.subplots_adjust()