diff --git a/src/newgrf_class_func.h b/src/newgrf_class_func.h
--- a/src/newgrf_class_func.h
+++ b/src/newgrf_class_func.h
@@ -63,7 +63,7 @@ DEFINE_NEWGRF_CLASS_METHOD(Tid)::Allocat
 		}
 	}
 
-	grfmsg(2, "ClassAllocate: already allocated %d classes, using default", Tmax);
+	GrfMsg(2, "ClassAllocate: already allocated {} classes, using default", Tmax);
 	return (Tid)0;
 }