diff --git a/ush/forecast_predet.sh b/ush/forecast_predet.sh
index e0c5b36ecc..bb1df19c2e 100755
--- a/ush/forecast_predet.sh
+++ b/ush/forecast_predet.sh
@@ -713,7 +713,6 @@ GOCART_predet(){
 
   if [[ ! -d "${COMOUT_CHEM_HISTORY}" ]]; then mkdir -p "${COMOUT_CHEM_HISTORY}"; fi
 
-  local aero_min=$(( FHROT > FHMIN ? FHROT + FHOUT_AERO : FHMIN + FHOUT_AERO ))
-
+  local aero_min=$(( ${FHROT:-0} > FHMIN ? FHROT + FHOUT_AERO : FHMIN + FHOUT_AERO ))
   GOCART_OUTPUT_FH=$(seq -s ' ' "$(( aero_min ))" "${FHOUT_AERO}" "${FHMAX}")
 }