diff --git a/bbb/boundary.m b/bbb/boundary.m
index a83b2be6..07cc44d6 100755
--- a/bbb/boundary.m
+++ b/bbb/boundary.m
@@ -210,7 +210,7 @@ cc                  if (fng_chem .ne. 0.) yldot(iv1) = -nurlxg*(
                   elseif (isnicore(ifld) .eq. 0) then # set flux to curcore
                      yldot(iv1) = - nurlxn* ( qe*
      .                       (fniy(ix,0,ifld)-fniycbo(ix,ifld))/sy(ix,0)
-     .                            - curcore(ifld)*gyf(ix,0)/sygytotc ) /
+     .                            - 2*curcore(ifld)*gyf(ix,0)/sygytotc ) /
      .                                              (qe*vpnorm*n0(ifld))
                   elseif (isnicore(ifld) .eq. 2) then # set flux & ni over range
                      yldot(iv1) = - nurlxn* ( qe*