diff --git a/libs/geom/include/psemek/geom/quaternion.hpp b/libs/geom/include/psemek/geom/quaternion.hpp
index c1ee3288..911f5a0d 100644
--- a/libs/geom/include/psemek/geom/quaternion.hpp
+++ b/libs/geom/include/psemek/geom/quaternion.hpp
@@ -226,14 +226,21 @@ namespace psemek::geom
 
 	// v0 & v1 assumed to be normalized
 	template <typename T>
-	quaternion<T> shortest_arc(vector<T, 3> const & v0, vector<T, 3> const & v1)
+	quaternion<T> shortest_arc(vector<T, 3> const & v0, vector<T, 3> const & v1, T const eps = T{1e-6})
 	{
 		auto axis = cross(v0, v1);
+		auto d = dot(v0, v1);
+
+		if (d + T{1} < eps)
+			axis = ort(v0);
+
 		quaternion<T> result;
+
 		result[0] = axis[0];
 		result[1] = axis[1];
 		result[2] = axis[2];
-		result[3] = T{1} + dot(v0, v1);
+		result[3] = T{1} + d;
+
 		result.coords = normalized(result.coords);
 		return result;
 	}