diff --git a/dumux/porousmediumflow/richards/iofields.hh b/dumux/porousmediumflow/richards/iofields.hh
index 8c53b02cd554abc07197c9598b8e06e04c2074f6..95c5fe4dbc740f31d5d66104d4de5502804d7b6d 100644
--- a/dumux/porousmediumflow/richards/iofields.hh
+++ b/dumux/porousmediumflow/richards/iofields.hh
@@ -68,7 +68,7 @@ public:
         if(gravity)
             out.addVolumeVariable([](const auto& v){ return v.pressureHead(FS::liquidPhaseIdx); },
                                   IOName::pressureHead());
-        if (enableWaterDiffusionInAir)
+        if constexpr (enableWaterDiffusionInAir)
             out.addVolumeVariable([](const auto& v){ return v.moleFraction(FS::gasPhaseIdx, FS::liquidCompIdx); },
                                   IOName::moleFraction<FS>(FS::gasPhaseIdx, FS::liquidCompIdx));
         out.addVolumeVariable([](const auto& v){ return v.waterContent(FS::liquidPhaseIdx); },
diff --git a/dumux/porousmediumflow/richards/localresidual.hh b/dumux/porousmediumflow/richards/localresidual.hh
index 748e978a43e416182807a176f57a262d02bf0238..50b2b812a61e193a4cade4be68e43ec30cab99aa 100644
--- a/dumux/porousmediumflow/richards/localresidual.hh
+++ b/dumux/porousmediumflow/richards/localresidual.hh
@@ -111,7 +111,7 @@ public:
                                * volVars.saturation(liquidPhaseIdx);
 
         // for extended Richards we consider water in air
-        if (enableWaterDiffusionInAir)
+        if constexpr (enableWaterDiffusionInAir)
             storage[conti0EqIdx] += volVars.porosity()
                                     * volVars.molarDensity(gasPhaseIdx)
                                     * volVars.moleFraction(gasPhaseIdx, liquidCompIdx)
@@ -155,7 +155,7 @@ public:
         flux[conti0EqIdx] = fluxVars.advectiveFlux(liquidPhaseIdx, upwindTerm);
 
         // for extended Richards we consider water vapor diffusion in air
-        if (enableWaterDiffusionInAir)
+        if constexpr (enableWaterDiffusionInAir)
         {
             //check for the reference system and adapt units of the diffusive flux accordingly.
             if (FluxVariables::MolecularDiffusionType::referenceSystemFormulation() == ReferenceSystemFormulation::massAveraged)