diff --git a/bob/learn/misc/isv_trainer.cpp b/bob/learn/misc/isv_trainer.cpp
index 0e91e8b9c06a1be0f5ca5d1ac4648c70f44fbe75..6ac3b83cae707b206f59a5b111338b2f3a5fd888 100644
--- a/bob/learn/misc/isv_trainer.cpp
+++ b/bob/learn/misc/isv_trainer.cpp
@@ -442,7 +442,7 @@ static auto m_step = bob::extension::FunctionDoc(
   "",
   true
 )
-.add_prototype("isv_base,stats")
+.add_prototype("isv_base")
 .add_parameter("isv_base", ":py:class:`bob.learn.misc.ISVBase`", "ISVBase Object");
 static PyObject* PyBobLearnMiscISVTrainer_m_step(PyBobLearnMiscISVTrainerObject* self, PyObject* args, PyObject* kwargs) {
   BOB_TRY
@@ -452,7 +452,7 @@ static PyObject* PyBobLearnMiscISVTrainer_m_step(PyBobLearnMiscISVTrainerObject*
 
   PyBobLearnMiscISVBaseObject* isv_base = 0;
 
-  if (!PyArg_ParseTupleAndKeywords(args, kwargs, "O!", kwlist, &PyBobLearnMiscISVBase_Type, &isv_base)) Py_RETURN_NONE;
+  if (!PyArg_ParseTupleAndKeywords(args, kwargs, "O!", kwlist, &PyBobLearnMiscISVBase_Type, &isv_base)) return 0;
 
   self->cxx->mStep(*isv_base->cxx);
 
diff --git a/bob/learn/misc/test_jfa_trainer.py b/bob/learn/misc/test_jfa_trainer.py
index c2505b2b61b67faae63398cef3f7e45950364400..4df6d00a867e2fda9bddba1a2b15f70688c5ab0a 100644
--- a/bob/learn/misc/test_jfa_trainer.py
+++ b/bob/learn/misc/test_jfa_trainer.py
@@ -231,7 +231,7 @@ def test_ISVTrainAndEnrol():
   mb.u = M_u
   for i in range(10):
     t.e_step(mb, TRAINING_STATS)
-    t.m_step(mb, TRAINING_STATS)
+    t.m_step(mb)
 
   assert numpy.allclose(mb.d, d_ref, eps)
   assert numpy.allclose(mb.u, u_ref, eps)