diff --git a/libs/geom/include/psemek/geom/quaternion.hpp b/libs/geom/include/psemek/geom/quaternion.hpp
index 3cbc2840..d9890e2e 100644
--- a/libs/geom/include/psemek/geom/quaternion.hpp
+++ b/libs/geom/include/psemek/geom/quaternion.hpp
@@ -305,6 +305,12 @@ namespace psemek::geom
 		return quaternion<T>{{v[0], v[1], v[2], std::log(n)}};
 	}
 
+	template <typename T, typename H>
+	quaternion<T> cast(quaternion<H> const & q)
+	{
+		return {cast<T>(q.coords)};
+	}
+
 	template <typename T>
 	std::ostream & operator << (std::ostream & os, quaternion<T> const & q)
 	{