diff --git a/mirgecom/wall_model.py b/mirgecom/wall_model.py
index 7011ad3ca..ee9c2f744 100644
--- a/mirgecom/wall_model.py
+++ b/mirgecom/wall_model.py
@@ -152,7 +152,7 @@ def density(self) -> DOFArray:
         """Return the wall density for all components."""
         return self._density_func()
 
-    def heat_capacity(self, temperature: DOFArray = None) -> DOFArray:
+    def heat_capacity(self, temperature: Optional[DOFArray] = None) -> DOFArray:
         """Return the wall heat_capacity for all components."""
         return self._heat_capacity_func(temperature)
 
@@ -161,7 +161,7 @@ def enthalpy(self, temperature: DOFArray) -> DOFArray:
         return self._enthalpy_func(temperature)
 
     def thermal_diffusivity(self, mass: DOFArray, temperature: DOFArray,
-            thermal_conductivity: DOFArray = None) -> DOFArray:
+            thermal_conductivity: Optional[DOFArray] = None) -> DOFArray:
         """Return the wall thermal diffusivity for all components."""
         if thermal_conductivity is None:
             thermal_conductivity = self.thermal_conductivity(temperature)
@@ -172,7 +172,7 @@ def thermal_conductivity(self, temperature: DOFArray) -> DOFArray:
         return self._thermal_conductivity_func(temperature)
 
     def get_temperature(self, wv: SolidWallConservedVars,
-            tseed: DOFArray = None, niter: int = 3) -> DOFArray:
+            tseed: Optional[DOFArray] = None, niter: int = 3) -> DOFArray:
         """Evaluate the temperature based on the energy."""
         if tseed is not None:
             temp = tseed*1.0
@@ -185,7 +185,8 @@ def get_temperature(self, wv: SolidWallConservedVars,
         return wv.energy/(self.density()*self.heat_capacity())
 
     def dependent_vars(self, wv: SolidWallConservedVars,
-            tseed: DOFArray = None, niter: int = 3) -> SolidWallDependentVars:
+            tseed: Optional[DOFArray] = None,
+                       niter: int = 3) -> SolidWallDependentVars:
         """Return solid wall dependent variables."""
         temperature = self.get_temperature(wv, tseed, niter)
         kappa = self.thermal_conductivity(temperature)
@@ -315,14 +316,14 @@ def bulk_viscosity(self, cv: ConservedVars, dv: GasDependentVars,
     def volume_viscosity(self, cv: ConservedVars, dv: GasDependentVars,
             wv: PorousWallVars, eos: GasEOS) -> DOFArray:
         r"""Get the 2nd viscosity coefficent, $\lambda$."""
-        return (self.bulk_viscosity(cv, dv, wv, eos)
-            - 2./3. * self.viscosity(cv, dv, wv, eos))
+        return (self.bulk_viscosity(cv, dv, wv, eos)  # type: ignore
+            - 2./3. * self.viscosity(cv, dv, wv, eos))  # type: ignore
 
     def viscosity(self, cv: ConservedVars, dv: GasDependentVars,
             wv: PorousWallVars, eos: GasEOS) -> DOFArray:
         """Viscosity of the gas through the porous wall."""
-        return 1.0/wv.void_fraction*(
-            self.base_transport.viscosity(cv, dv, eos))
+        return 1.0/wv.void_fraction*(  # type: ignore
+            self.base_transport.viscosity(cv, dv, eos))  # type: ignore
 
     def thermal_conductivity(self, cv: ConservedVars, dv: GasDependentVars,
             wv: PorousWallVars, eos: GasEOS,
@@ -340,12 +341,13 @@ def thermal_conductivity(self, cv: ConservedVars, dv: GasDependentVars,
         """
         kappa_s = wall_eos.thermal_conductivity(dv.temperature, wv.tau)
         kappa_g = self.base_transport.thermal_conductivity(cv, dv, eos)
-        return (wv.density*kappa_s + cv.mass*kappa_g)/(cv.mass + wv.density)
+        return (wv.density*kappa_s + cv.mass*kappa_g)/(cv.mass + wv.density)\
+            # type: ignore
 
     def species_diffusivity(self, cv: ConservedVars, dv: GasDependentVars,
-            wv: PorousWallVars, eos: GasEOS) -> DOFArray:
+            wv: PorousWallVars, eos: GasEOS) -> np.ndarray:
         """Mass diffusivity of gaseous species through the porous wall."""
-        return 1.0/wv.tortuosity*(
+        return 1.0/wv.tortuosity*(  # type: ignore
             self.base_transport.species_diffusivity(cv, dv, eos))
 
     def transport_vars(self, cv: ConservedVars, dv: GasDependentVars,
@@ -355,8 +357,8 @@ def transport_vars(self, cv: ConservedVars, dv: GasDependentVars,
         return GasTransportVars(
             bulk_viscosity=self.bulk_viscosity(cv, dv, wv, eos),
             viscosity=self.viscosity(cv, dv, wv, eos),
-            thermal_conductivity=self.thermal_conductivity(cv, dv, wv, eos,
-                                                           wall_eos),
+            thermal_conductivity=self.thermal_conductivity(  # type: ignore
+                cv, dv, wv, eos, wall_eos),
             species_diffusivity=self.species_diffusivity(cv, dv, wv, eos)
         )