diff --git a/comupp/src/unipost/CALTAU.f b/comupp/src/unipost/CALTAU.f
index 381452245..222c4e10f 100644
--- a/comupp/src/unipost/CALTAU.f
+++ b/comupp/src/unipost/CALTAU.f
@@ -125,7 +125,7 @@ SUBROUTINE CALTAU(TAUX,TAUY)
 !     
 !       COMPUTE U (EGRIDU) AND V (EGRIDV) WIND STRESSES.
 !
-        ELSQR     = EL(I,J,LMHK)*EL(I,J,LMHK)
+        ELSQR     = EL(I,J,LMHK-1)*EL(I,J,LMHK-1)
         TAUX(I,J) = RHO*ELSQR*DELUDZ*DELUDZ
         TAUY(I,J) = RHO*ELSQR*DELVDZ*DELVDZ