diff --git a/sorc/chgres_cube.fd/atm_input_data.F90 b/sorc/chgres_cube.fd/atm_input_data.F90
index cb9b1e87c..bf5494b72 100644
--- a/sorc/chgres_cube.fd/atm_input_data.F90
+++ b/sorc/chgres_cube.fd/atm_input_data.F90
@@ -2154,13 +2154,19 @@ subroutine read_input_atm_grib2_file(localpet)
 
  call quicksort(rlevs,1,lev_input)
 
- do i = 1, lev_input
+ do i = 1, lev_input     
    if (isnative) then
      write(slevs(i), '(i6)') nint(rlevs(i))
      slevs(i) = trim(slevs(i)) // " hybrid"
+     if (i>1) then
+       if (any(slevs(1:i-1)==slevs(i))) call error_handler("Duplicate vertical level entries found.",1)
+     endif
    else
      write(slevs(i), '(f11.2)') rlevs(i)
      slevs(i) = trim(slevs(i)) // " Pa"
+     if (i>1) then
+       if (any(slevs(1:i-1)==slevs(i))) call error_handler("Duplicate vertical level entries found.",1)
+     endif
    endif
  enddo