diff --git a/src/binary_c_python.c b/src/binary_c_python.c
index 7ecc09f0e1367efec821c2dd6ee4429d15810310..dd184d5fdd5271f09d6556c51e73248578b52374 100644
--- a/src/binary_c_python.c
+++ b/src/binary_c_python.c
@@ -260,6 +260,8 @@ static PyObject* binary_c_run_system(PyObject *self, PyObject *args, PyObject *k
     Safe_free(buffer);
     Safe_free(error_buffer);
 
+    // TODO: fix that the return_error_string is returned.
+
     return return_string;
 }
 
diff --git a/tests/population/test_population.py b/tests/population/test_population.py
index a43d96917456bc855a5cf0faf6cb19b092c13235..6393d239af3fc85144d9607796bc31056249387a 100644
--- a/tests/population/test_population.py
+++ b/tests/population/test_population.py
@@ -38,6 +38,8 @@ def parse_function(self, output):
     for i in range(16):
         mass_lost_dict['{}'.format(i)] = 0
 
+    total_mass_lost = 0
+
     # Go over the output.
     for el in output_lines(output):
         headerline = el.split()[0]