diff --git a/dumux/flux/box/fickslaw.hh b/dumux/flux/box/fickslaw.hh
index 563ad422ee87b3580deb6ab3e7273d85aed6557a..0465c9bbaf61317084ceab0b04c6cb58841688ef 100644
--- a/dumux/flux/box/fickslaw.hh
+++ b/dumux/flux/box/fickslaw.hh
@@ -123,7 +123,7 @@ public:
             // compute the diffusive flux
             componentFlux[compIdx] = -1.0*rho*vtmv(scvf.unitOuterNormal(), D, gradX)*scvf.area();
             if (BalanceEqOpts::mainComponentIsBalanced(phaseIdx) && !FluidSystem::isTracerFluidSystem())
-                componentFlux[phaseIdx] -= componentFlux[compIdx];
+                componentFlux[FluidSystem::getMainComponent(phaseIdx)] -= componentFlux[compIdx];
         }
         return componentFlux;
     }