diff --git a/tasks/flightradar24/ingest/mart/build_mart.py b/tasks/flightradar24/ingest/mart/build_mart.py
index d64cb6d..f682cb9 100644
--- a/tasks/flightradar24/ingest/mart/build_mart.py
+++ b/tasks/flightradar24/ingest/mart/build_mart.py
@@ -408,7 +408,7 @@ def insert_mart_points(conn, mart_flight_id: int, points: List[Dict],
 
         args = []
         for p in points:
-            alt_m = p.get("altitude_m") or 0
+            alt_m = float(p.get("altitude_m") or 0)
             alt_ft = alt_m / FT_TO_M
             noise = altitude_to_noise_db(alt_ft, aircraft_type or "default")
             args.append((