diff --git a/features/communication.py b/features/communication.py
index 66dfa07..69eb319 100644
--- a/features/communication.py
+++ b/features/communication.py
@@ -88,7 +88,20 @@ def enumerate_contacts(comm_df: pd.DataFrame) -> pd.DataFrame:
 
 
 def count_comms(comm_df: pd.DataFrame) -> pd.DataFrame:
+    """
+    Calculate frequencies (and duration) of messages (or calls), grouped by their types.
 
+    Parameters
+    ----------
+    comm_df: pd.DataFrame
+        A dataframe of calls or SMSes.
+
+    Returns
+    -------
+    comm_features: pd.DataFrame
+        A list of communication features for every participant.
+
+    """
     if "call_type" in comm_df:
         comm_counts = (
             comm_df.value_counts(subset=["participant_id", "call_type"])
@@ -104,6 +117,11 @@ def count_comms(comm_df: pd.DataFrame) -> pd.DataFrame:
             .add_prefix("duration_")
         )
         comm_features = comm_counts.join(comm_duration)
+        try: comm_features.drop(columns="duration_" + call_types[3], inplace=True)
+        # The missed calls are always of 0 duration.
+        except KeyError: pass
+        # If there were no missed calls, this exception is raised.
+        # But we are dropping the column anyway, so no need to deal with the exception.
     elif "message_type" in comm_df:
         comm_counts = (
             comm_df.value_counts(subset=["participant_id", "message_type"])