diff --git a/src/activity_parser/activity.py b/src/activity_parser/activity.py
index aa518da..ef492a7 100644
--- a/src/activity_parser/activity.py
+++ b/src/activity_parser/activity.py
@@ -123,7 +123,7 @@ def fill_activity(activity: Activity, records: pd.DataFrame, laps: pd.DataFrame)
         "avg_power": _aggregate(records, "power", "mean"),
         "max_power": _aggregate(records, "power", "max"),
         "avg_cadence": _aggregate(records, "cadence", "mean", skip_zeros=True),
-        "max_cadence": _aggregate(records, "cadence", "max"),
+        "max_cadence": _aggregate(records, "cadence", "max", skip_zeros=True),
     }
 
     to_fill = {
diff --git a/tests/test_activity.py b/tests/test_activity.py
index 3c26c81..2af1d03 100644
--- a/tests/test_activity.py
+++ b/tests/test_activity.py
@@ -17,6 +17,15 @@ def test_avg_power_keeps_zero_samples_avg_cadence_drops_them():
     assert activity.avg_cadence == 82.0
 
 
+def test_all_zero_power_column_reports_zero_all_zero_cadence_column_reports_none():
+    records = pd.DataFrame({"power": [0.0, 0.0], "cadence": [0.0, 0.0]})
+    result = fill_activity(Activity(), records, pd.DataFrame())
+    assert result.avg_power == 0.0
+    assert result.max_power == 0.0
+    assert result.avg_cadence is None
+    assert result.max_cadence is None
+
+
 def test_fill_activity_ignores_lap_level_sensor_summaries():
     # A lap sensor summary can silently be 0 when unpaired; only records are trusted.
     laps = pd.DataFrame({"max_heart_rate": [150.0, 160.0], "max_speed": [30.0, 25.0]})