diff --git a/src/newgrf_cargo.cpp b/src/newgrf_cargo.cpp
--- a/src/newgrf_cargo.cpp
+++ b/src/newgrf_cargo.cpp
@@ -19,7 +19,7 @@
 struct CargoResolverObject : public ResolverObject {
 	CargoResolverObject(const CargoSpec *cs, CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
-	/* virtual */ const SpriteGroup *ResolveReal(const RealSpriteGroup *group) const;
+	const SpriteGroup *ResolveReal(const RealSpriteGroup *group) const override;
 };
 
 /* virtual */ const SpriteGroup *CargoResolverObject::ResolveReal(const RealSpriteGroup *group) const