diff --git a/src/GCHP_GridComp/GCHPctmEnv_GridComp/GCHPctmEnv_GridCompMod.F90 b/src/GCHP_GridComp/GCHPctmEnv_GridComp/GCHPctmEnv_GridCompMod.F90
index d7f424d59..b62d2500c 100644
--- a/src/GCHP_GridComp/GCHPctmEnv_GridComp/GCHPctmEnv_GridCompMod.F90
+++ b/src/GCHP_GridComp/GCHPctmEnv_GridComp/GCHPctmEnv_GridCompMod.F90
@@ -953,8 +953,9 @@ subroutine prepare_massflux_exports(IMPORT, EXPORT, PLE, dt, RC)
          ! Get vertical mass flux
          call fv_getVerticalMassFlux(MFX_EXPORT, MFY_EXPORT, UpwardsMassFlux, dt)
 
-         ! Flip vertical so that GCHP diagnostic is positive="up"
-         UpwardsMassFlux(:,:,:) = UpwardsMassFlux(:,:,LM:0:-1)/dt
+         ! Flip vertical so that GCHP diagnostic level is follwing GEOS-Chem convetion
+         ! Add negative sign to make positive = "up"
+         UpwardsMassFlux(:,:,:) = -UpwardsMassFlux(:,:,LM:0:-1)/dt
       end if
 
       ! nullify pointers