diff --git a/backend/src/services/vehicle.service.ts b/backend/src/services/vehicle.service.ts
index 79b195a..0b0cf55 100644
--- a/backend/src/services/vehicle.service.ts
+++ b/backend/src/services/vehicle.service.ts
@@ -445,7 +445,10 @@ class VehicleService {
          ORDER BY faellig_am DESC, created_at DESC`,
         [fahrzeugId]
       );
-      return result.rows as FahrzeugPruefung[];
+      return result.rows.map(r => ({
+        ...r,
+        kosten: r.kosten != null ? Number(r.kosten) : null,
+      })) as FahrzeugPruefung[];
     } catch (error) {
       logger.error('VehicleService.getPruefungenForVehicle failed', { error, fahrzeugId });
       throw new Error('Failed to fetch inspection history');
@@ -546,7 +549,10 @@ class VehicleService {
          ORDER BY datum DESC, created_at DESC`,
         [fahrzeugId]
       );
-      return result.rows as FahrzeugWartungslog[];
+      return result.rows.map(r => ({
+        ...r,
+        kosten: r.kosten != null ? Number(r.kosten) : null,
+      })) as FahrzeugWartungslog[];
     } catch (error) {
       logger.error('VehicleService.getWartungslogForVehicle failed', { error, fahrzeugId });
       throw new Error('Failed to fetch maintenance log');