diff --git a/src/oce_ale_mixing_kpp.F90 b/src/oce_ale_mixing_kpp.F90
index c7204cd46..4a5976bc5 100755
--- a/src/oce_ale_mixing_kpp.F90
+++ b/src/oce_ale_mixing_kpp.F90
@@ -875,8 +875,8 @@ subroutine ddmix(diffK, tracers, partit, mesh)
         nzmin = ulevels_nod2D(node)
         nzmax = nlevels_nod2D(node)
         DO nz=nzmin+1,nzmax-1
-           alphaDT = sw_alpha(nz-1,node) * tracers%data(1)%values(nz-1,node)
-           betaDS  = sw_beta (nz-1,node) * tracers%data(2)%values(nz-1,node)
+           alphaDT = sw_alpha(nz-1,node) * (tracers%data(1)%values(nz-1,node) - tracers%data(1)%values(nz,node))
+           betaDS  = sw_beta (nz-1,node) * (tracers%data(2)%values(nz-1,node) - tracers%data(2)%values(nz,node))
 
            IF (alphaDT > betaDS .and. betaDS > 0.0_WP) THEN