diff --git a/dumux/material/fluidsystems/h2oair.hh b/dumux/material/fluidsystems/h2oair.hh
index 2768b4abb88d71fddd9745a145f9967107bb0ec9..900f74a90105e7b015c11d35cf3dd82d44f99162 100644
--- a/dumux/material/fluidsystems/h2oair.hh
+++ b/dumux/material/fluidsystems/h2oair.hh
@@ -493,11 +493,9 @@ public:
                     Scalar divisor = 0;
                     for (int j = 0; j < numComponents; ++j)
                     {
-                        Scalar phiIJ = 1 + sqrt(mu[i]/mu[j]) * // 1 + (mu[i]/mu[j]^1/2
-                            pow(M[j]/M[i], 1./4.0);   // (M[i]/M[j])^1/4
-
-                        phiIJ *= phiIJ;
-                        phiIJ /= sqrt(8*(1 + M[i]/M[j]));
+                        // 1 + (mu[i]/mu[j]^1/2 * (M[i]/M[j])^1/4)
+                        Scalar phiIJ = 1 + sqrt(mu[i]/mu[j] * sqrt(M[j]/M[i]));
+                        phiIJ = phiIJ * phiIJ / sqrt(8*(1 + M[i]/M[j]));
                         divisor += fluidState.moleFraction(phaseIdx, j)*phiIJ;
                     }
                     muResult += fluidState.moleFraction(phaseIdx, i)*mu[i] / divisor;