diff --git a/agenda/utils.py b/agenda/utils.py
index 1b03fc3..ff311d0 100644
--- a/agenda/utils.py
+++ b/agenda/utils.py
@@ -7,20 +7,24 @@ DateOrDateTime = datetime | date
 
 def as_date(d: DateOrDateTime) -> date:
     """Convert datetime to date."""
-    if isinstance(d, datetime):
-        return d.date()
-    assert isinstance(d, date)
-    return d
+    match d:
+        case datetime():
+            return d.date()
+        case date():
+            return d
+        case _:
+            raise TypeError(f"Unsupported type: {type(d)}")
 
 
 def as_datetime(d: DateOrDateTime) -> datetime:
     """Date/time of event."""
-    t0 = datetime.min.time()
-    return (
-        d
-        if isinstance(d, datetime)
-        else datetime.combine(d, t0).replace(tzinfo=timezone.utc)
-    )
+    match d:
+        case datetime():
+            return d
+        case date():
+            return datetime.combine(d, datetime.min.time()).replace(tzinfo=timezone.utc)
+        case _:
+            raise TypeError(f"Unsupported type: {type(d)}")
 
 
 def human_readable_delta(future_date: date) -> str | None: