diff --git a/frontend/src/features/vehicles/mobile/VehicleDetailMobile.tsx b/frontend/src/features/vehicles/mobile/VehicleDetailMobile.tsx
index bef18a7..b241054 100644
--- a/frontend/src/features/vehicles/mobile/VehicleDetailMobile.tsx
+++ b/frontend/src/features/vehicles/mobile/VehicleDetailMobile.tsx
@@ -142,7 +142,9 @@ export const VehicleDetailMobile: React.FC<VehicleDetailMobileProps> = ({
         secondaryParts.push(new Date(rec.date).toLocaleDateString());
         secondaryParts.push('Maintenance');
         const secondary = secondaryParts.join(' • ');
-        const amount = typeof rec.cost === 'number' ? `$${rec.cost.toFixed(2)}` : undefined;
+        // Backend returns numeric/decimal columns as strings via node-postgres; coerce.
+        const costNum = rec.cost != null ? Number(rec.cost) : NaN;
+        const amount = Number.isFinite(costNum) ? `$${costNum.toFixed(2)}` : undefined;
         list.push({
           id: rec.id,
           type: 'Maintenance',
diff --git a/frontend/src/features/vehicles/pages/VehicleDetailPage.tsx b/frontend/src/features/vehicles/pages/VehicleDetailPage.tsx
index 65e7e0f..4bdce5b 100644
--- a/frontend/src/features/vehicles/pages/VehicleDetailPage.tsx
+++ b/frontend/src/features/vehicles/pages/VehicleDetailPage.tsx
@@ -148,7 +148,9 @@ export const VehicleDetailPage: React.FC = () => {
         if (subtypeText) parts.push(subtypeText);
         if (rec.shopName) parts.push(rec.shopName);
         const summary = parts.join(' • ');
-        const amount = typeof rec.cost === 'number' ? `$${rec.cost.toFixed(2)}` : undefined;
+        // Backend returns numeric/decimal columns as strings via node-postgres; coerce.
+        const costNum = rec.cost != null ? Number(rec.cost) : NaN;
+        const amount = Number.isFinite(costNum) ? `$${costNum.toFixed(2)}` : undefined;
         list.push({ id: rec.id, type: 'Maintenance', date: rec.date, summary, amount });
       }
     }