diff --git a/parm/config/gefs/yaml/defaults.yaml b/parm/config/gefs/yaml/defaults.yaml
index f0e8772b67..cda90c5485 100644
--- a/parm/config/gefs/yaml/defaults.yaml
+++ b/parm/config/gefs/yaml/defaults.yaml
@@ -31,4 +31,6 @@ stage_ic:
   USE_ATM_ENS_PERTURB_FILES: "NO"
 ocn:
   MOM6_INTERP_ICS: "NO"
-
+# config.aero has just a system-specific path to add.
+# This is handled by the setup_expt.py, but it has to be told to write to it.
+aero: {}