diff --git a/examples/scripts/spme_max_energy.py b/examples/scripts/spme_max_energy.py
index 398715b15..8f54484b8 100644
--- a/examples/scripts/spme_max_energy.py
+++ b/examples/scripts/spme_max_energy.py
@@ -156,7 +156,8 @@ def _evaluate(self, x, grad=None):
                 gravimetric_energy_density_Ah = np.trapz(voltage * current) / (
                     3600 * cell_mass(self.problem._model._parameter_set)
                 )
-                # Take negative in order to maximise energy density
+                # Return the negative energy density, as the optimiser minimises
+                # this function, to carry out maximisation of the energy density
                 return -gravimetric_energy_density_Ah