diff --git a/src/MNH/gravity_impl.f90 b/src/MNH/gravity_impl.f90
index c1820f7e4da19976313b01dfbf59b5f4ac5cf91a..f42d6009cf9994b7978cf922aa887c195c491d82 100644
--- a/src/MNH/gravity_impl.f90
+++ b/src/MNH/gravity_impl.f90
@@ -123,6 +123,7 @@ INTEGER :: JR
 !-------------------------------------------------------------------------------
 !
 ZRWS_GRAV = 0.
+ZR = 0.
 !
 ! guess of Theta at future time-step
 ZTH(:,:,:) = (PRTHS(:,:,:) + PRTHS_CLD(:,:,:)) / PRHODJ * PTSTEP