diff --git a/dumux/flux/box/fickslaw.hh b/dumux/flux/box/fickslaw.hh
index 6ff46447c4af8f228c58ed247314da2851d832b0..b893f3b1d9df4469d10e69f3751992b2d3d99441 100644
--- a/dumux/flux/box/fickslaw.hh
+++ b/dumux/flux/box/fickslaw.hh
@@ -175,7 +175,7 @@ private:
     }
 
     static std::pair<Scalar, Scalar>
-    diffusionCoefficientsAtInterface_(const int phaseIdx, const int compIdx,
+    diffusionCoefficientsAtInterface_([[maybe_unused]] const int phaseIdx, const int compIdx,
                                       const VolumeVariables& insideVV, const VolumeVariables& outsideVV)
     {
         if constexpr (!FluidSystem::isTracerFluidSystem())