diff --git a/libs/geom/include/psemek/geom/interval.hpp b/libs/geom/include/psemek/geom/interval.hpp
index 79f89af3..0ccc0a63 100644
--- a/libs/geom/include/psemek/geom/interval.hpp
+++ b/libs/geom/include/psemek/geom/interval.hpp
@@ -124,6 +124,12 @@ namespace psemek::geom
 		return {static_cast<T1>(i.min), static_cast<T1>(i.max)};
 	}
 
+	template <typename T>
+	interval<T> operator - (interval<T> const & i)
+	{
+		return {-i.max, -i.min};
+	}
+
 	template <typename T>
 	interval<T> operator + (interval<T> const & i, T const & delta)
 	{
@@ -142,6 +148,12 @@ namespace psemek::geom
 		return {i.min - delta, i.max - delta};
 	}
 
+	template <typename T>
+	interval<T> operator - (T const & delta, interval<T> const & i)
+	{
+		return {delta - i.max, delta - i.min};
+	}
+
 	template <typename T>
 	interval<T> operator & (interval<T> const & i, T const & a)
 	{