diff --git a/libs/geom/include/psemek/geom/orthographic.hpp b/libs/geom/include/psemek/geom/orthographic.hpp
index 0748008c..d508efcb 100644
--- a/libs/geom/include/psemek/geom/orthographic.hpp
+++ b/libs/geom/include/psemek/geom/orthographic.hpp
@@ -94,8 +94,8 @@ namespace psemek::geom
 	{
 		auto inv = [](interval<T> const & i)
 		{
-			auto const s = i.length();
-			auto const d = i.max - i.min;
+			auto const s = i.min + i.max;
+			auto const d = i.length();
 			return interval<T>{ (- s - 2) / d, (- s + 2) / d };
 		};