diff --git a/interface/multifluid.cpp b/interface/multifluid.cpp
index 46a5a2fe4e71b43486eb7ad33858d0a5a3205589..2d027ea6ae15298f7159251ac1339daf3ee022ae 100644
--- a/interface/multifluid.cpp
+++ b/interface/multifluid.cpp
@@ -13,6 +13,7 @@ void add_AmmoniaWaterTillnerRoth(py::module&m ){
         .def(py::init<>())
         .def_readonly("TcNH3", &AmmoniaWaterTillnerRoth::TcNH3)
         .def_readonly("vcNH3", &AmmoniaWaterTillnerRoth::vcNH3)
+        .def("alphar_departure", &AmmoniaWaterTillnerRoth::alphar_departure<double, double, double>, py::arg("tau"), py::arg("delta"), py::arg("xNH3"))
     ;
     add_derivatives<AmmoniaWaterTillnerRoth>(m, wAW);
 }