diff --git a/src/newgrf_engine.cpp b/src/newgrf_engine.cpp
index 40d931d70d..f13543f087 100644
--- a/src/newgrf_engine.cpp
+++ b/src/newgrf_engine.cpp
@@ -561,7 +561,7 @@ static uint32 VehicleGetVariable(Vehicle *v, const ResolverObject *object, byte
 					airporttype = st->airport.GetSpec()->ttd_airport_type;
 				}
 
-				return (altitude << 8) | airporttype;
+				return (Clamp(altitude, 0, 0xFF) << 8) | airporttype;
 			}
 
 		case 0x45: { // Curvature info