diff --git a/cime_config/namelist_definition_drv.xml b/cime_config/namelist_definition_drv.xml
index 8835c53b8..ec437189e 100644
--- a/cime_config/namelist_definition_drv.xml
+++ b/cime_config/namelist_definition_drv.xml
@@ -910,13 +910,14 @@
     <valid_values>ogrid,agrid,xgrid</valid_values>
     <desc>
       Grid for atm ocn flux calc
-      default: ogrid
+      default: xgrid for fully coupled cases, ogrid for datm
     </desc>
     <values>
       <value>xgrid</value>
       <!-- xgrid introduces unnecessary cost and complexity if atm & ocn are on the same
       grid, so fall back to ogrid in that case -->
       <value samegrid_atm_ocn='true'>ogrid</value>
+      <value COMP_ATM='datm'>ogrid</value>
     </values>
   </entry>
   <entry id="ocn_surface_flux_scheme">