diff --git a/src/SURFEX/prep_isba_ascllv.F90 b/src/SURFEX/prep_isba_ascllv.F90
index 3b9ba798d4992d3a46205ac5e198381b7d45d8bd..561e33e051493f3eb1f668839b92efdbeed09996 100644
--- a/src/SURFEX/prep_isba_ascllv.F90
+++ b/src/SURFEX/prep_isba_ascllv.F90
@@ -91,6 +91,11 @@ REAL(KIND=JPRB) :: ZHOOK_HANDLE
 !
 IF (LHOOK) CALL DR_HOOK('PREP_ISBA_ASCLLV',0,ZHOOK_HANDLE)
 !
+IF ((.NOT.ALLOCATED(NINDEX)).AND.(HPROGRAM=='MESONH')) THEN 
+  ALLOCATE(NINDEX(U%NDIM_FULL))
+  NINDEX(:) = 0
+ENDIF
+!
 IF (.NOT.ALLOCATED(NNUM)) THEN
   ALLOCATE(NNUM(U%NDIM_FULL))
   IF (NRANK/=NPIO) THEN