diff --git a/neEqn.H b/neEqn.H
index 6dcc746..54f051b 100644
--- a/neEqn.H
+++ b/neEqn.H
@@ -6,22 +6,21 @@
         Te = T;
         Te.correctBoundaryConditions();
 
-        scalarField X (csSpecies.size(), 0.0);
         scalarField &W (csSpeciesW);
 
         forAll (Te, cid)
         {
-            scalar eEps = (3./2.) * kB.value() * Te[cid]
-                / eCharge.value();
+            scalar eEps = (3./2.) * kB.value() * Te[cid] / eCharge.value();
+            scalar sumX = 0.0;
 
             sigma_m[cid] = 0;
             forAll (csSpecies, isp)
             {
-                X[isp] = Y[csSpeciesI[isp]][cid]/W[isp];
-                sigma_m[cid] +=
-                    X[isp] * csList[isp].value(eEps);
+                scalar Xi = Y[csSpeciesI[isp]][cid]/W[isp];
+                sumX += Xi;
+                sigma_m[cid] += Xi * csList[isp].value(eEps);
             }
-            sigma_m[cid] /= sum(X);
+            sigma_m[cid] /= sumX;
         }
 
         Info <<  min(sigma_m) << " / " << max(sigma_m) << endl;