diff --git a/tardis/plasma/properties/nlte_rate_equation_solver.py b/tardis/plasma/properties/nlte_rate_equation_solver.py
index f6adb515d48..a4be8a98b44 100644
--- a/tardis/plasma/properties/nlte_rate_equation_solver.py
+++ b/tardis/plasma/properties/nlte_rate_equation_solver.py
@@ -672,7 +672,7 @@ def solution_vector_block(self, atomic_number, number_density):
         return solution_vector
 
     def prepare_solution_vector(self, number_density):
-        """Constructs the solution vector for the NLTE ionization solver set of equations by combining 
+        """Constructs the solution vector for the NLTE ionization solver set of equations by combining
         all solution verctor blocks.
 
         Parameters
diff --git a/tardis/plasma/tests/test_nlte_solver.py b/tardis/plasma/tests/test_nlte_solver.py
index 50178029066..fe2ee8fe685 100644
--- a/tardis/plasma/tests/test_nlte_solver.py
+++ b/tardis/plasma/tests/test_nlte_solver.py
@@ -291,16 +291,21 @@ def nlte_raw_plasma(tardis_model_config_nlte, nlte_raw_model, nlte_atom_data):
 
 
 def test_critical_case(nlte_raw_plasma):
-    """Compares the LTE solution with NLTE solution at a critical value of w=1.0.
-    """
+    """Compares the LTE solution with NLTE solution at a critical value of w=1.0."""
     ion_number_density_nlte = nlte_raw_plasma.ion_number_density_nlte.values
     ion_number_density_nlte[ion_number_density_nlte < 1e-10] = 0.0
 
     ind = IonNumberDensity(nlte_raw_plasma)
-    ion_number_density_lte  = ind.calculate(nlte_raw_plasma.thermal_phi_lte, nlte_raw_plasma.partition_function, nlte_raw_plasma.number_density)[0]
+    ion_number_density_lte = ind.calculate(
+        nlte_raw_plasma.thermal_phi_lte,
+        nlte_raw_plasma.partition_function,
+        nlte_raw_plasma.number_density,
+    )[0]
 
     ion_number_density_lte = ion_number_density_lte.values
-    ion_number_density_lte[ion_number_density_lte < 1e-10] = 0.0 #getting rid of small numbers.
+    ion_number_density_lte[
+        ion_number_density_lte < 1e-10
+    ] = 0.0  # getting rid of small numbers.
     assert_allclose(
         ion_number_density_lte,
         ion_number_density_nlte,