diff --git a/nifty_gridder.cc b/nifty_gridder.cc
index e499fbd8ac668e87c4e7117523405cbbc96d9c0f..0801bc0bb4453bbbbb4ea89ac22fc686eceb0ea5 100644
--- a/nifty_gridder.cc
+++ b/nifty_gridder.cc
@@ -1399,7 +1399,7 @@ PYBIND11_MODULE(nifty_gridder, m)
   m.def("grid2ms_wgt",&grid2ms_wgt<double>, "baselines"_a, "gconf"_a, "idx"_a,
     "grid"_a, "wgt"_a, "ms_in"_a=None);
   m.def("vis2grid_c",&vis2grid_c<double>, vis2grid_c_DS, "baselines"_a,
-    "gconf"_a, "idx"_a, "vis"_a, "grid_in"_a);
+    "gconf"_a, "idx"_a, "vis"_a, "grid_in"_a=None);
   m.def("ms2grid_c",&ms2grid_c<double>, ms2grid_c_DS, "baselines"_a, "gconf"_a,
     "idx"_a, "ms"_a, "grid_in"_a=None);
   m.def("ms2grid_c_wgt",&ms2grid_c_wgt<double>, "baselines"_a, "gconf"_a,