diff --git a/src/ground_vehicle.cpp b/src/ground_vehicle.cpp
index 97e21bafe1..ca8fe65fcf 100644
--- a/src/ground_vehicle.cpp
+++ b/src/ground_vehicle.cpp
@@ -110,7 +110,7 @@ int GroundVehicle<T, Type>::GetAcceleration() const
 	int64_t speed = v->GetCurrentSpeed(); // [km/h-ish]
 
 	/* Weight is stored in tonnes. */
-	int32_t mass = this->gcache.cached_weight;
+	int64_t mass = this->gcache.cached_weight;
 
 	/* Power is stored in HP, we need it in watts.
 	 * Each vehicle can have U16 power, 128 vehicles, HP -> watt