diff --git a/libs/geom/include/psemek/geom/intersection.hpp b/libs/geom/include/psemek/geom/intersection.hpp
index 9af61ace..f332dddc 100644
--- a/libs/geom/include/psemek/geom/intersection.hpp
+++ b/libs/geom/include/psemek/geom/intersection.hpp
@@ -183,6 +183,8 @@ namespace psemek::geom
 
 		if (sum > T{1}) return std::nullopt;
 
+		if (b[0] < T{}) return std::nullopt;
+
 		return b[0];
 	}