diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index 2a162426c8..67e233f9d7 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -689,6 +689,7 @@ static CommandCost CmdBuildRailWagon(DoCommandFlag flags, TileIndex tile, const
 /** Move all free vehicles in the depot to the train */
 void NormalizeTrainVehInDepot(const Train *u)
 {
+	assert(u->IsEngine());
 	for (const Train *v : Train::Iterate()) {
 		if (v->IsFreeWagon() && v->tile == u->tile &&
 				v->track == TRACK_BIT_DEPOT) {
diff --git a/src/vehicle_cmd.cpp b/src/vehicle_cmd.cpp
index 46f284e15c..549bd189c4 100644
--- a/src/vehicle_cmd.cpp
+++ b/src/vehicle_cmd.cpp
@@ -172,7 +172,7 @@ std::tuple<CommandCost, VehicleID, uint, uint16_t, CargoArray> CmdBuildVehicle(D
 		}
 
 		if (flags & DC_EXEC) {
-			if (type == VEH_TRAIN && use_free_vehicles && !(flags & DC_AUTOREPLACE)) {
+			if (type == VEH_TRAIN && use_free_vehicles && !(flags & DC_AUTOREPLACE) && Train::From(v)->IsEngine()) {
 				/* Move any free wagons to the new vehicle. */
 				NormalizeTrainVehInDepot(Train::From(v));
 			}