diff --git a/src/dynamics/none/dyn_grid.F90 b/src/dynamics/none/dyn_grid.F90
index 8d2b0431..64cc20b8 100644
--- a/src/dynamics/none/dyn_grid.F90
+++ b/src/dynamics/none/dyn_grid.F90
@@ -62,13 +62,15 @@ subroutine model_grid_init()
       use pio,              only: PIO_BCAST_ERROR, pio_seterrorhandling
       use pio,              only: pio_get_var, pio_freedecomp
       use pio,              only: pio_read_darray
+      use pio,              only: pio_inq_vartype, PIO_NOERR
       use spmd_utils,       only: npes, iam
       use cam_pio_utils,    only: cam_pio_handle_error, cam_pio_find_var
       use cam_pio_utils,    only: cam_pio_var_info, pio_subsystem
       use cam_pio_utils,    only: cam_pio_newdecomp
       use cam_abortutils,   only: endrun
       use cam_logfile,      only: cam_log_multiwrite
-      use cam_initfiles,    only: initial_file_get_id
+      use cam_initfiles,    only: initial_file_get_id, unset_path_str
+      use phys_comp,        only: ncdata_check
       use vert_coord,       only: vert_coord_init, pver
       use hycoef,           only: hycoef_init, hypi, hypm, nprlev, &
                                   hyam, hybm, hyai, hybi, ps0
@@ -107,6 +109,7 @@ subroutine model_grid_init()
       character(len=8)                  :: lat_dim_name
       character(len=8)                  :: lon_dim_name
       character(len=128)                :: errormsg
+      integer                           :: xtype
 
       character(len=*),  parameter :: subname = 'model_grid_init'
 
@@ -225,6 +228,27 @@ subroutine model_grid_init()
                                        'eastward_wind' /),                    &
                             fieldname, vardesc, var_found)
       if (var_found) then
+         ! Check that snapshot file has 64-bit floats (ndens=1).
+         ! Running with 32-bit (FLOAT32) snapshots will definitely cause
+         ! answer differences between CAM-SIMA and the CAM snapshot
+         ! leading to wasted debugging time, so disallow this configuration.
+         ! Only check when running a snapshot test (ncdata_check is set),
+         ! since the null dycore may also be used for other purposes
+         ! (e.g. single-column model) where lower-precision data is fine.
+         if (trim(ncdata_check) /= trim(unset_path_str)) then
+            iret = pio_inq_vartype(fh_ini, vardesc, xtype)
+            if (iret /= PIO_NOERR) then
+               call endrun(subname//': Unable to inquire variable type for '// &
+                    trim(fieldname))
+            end if
+            if (xtype /= PIO_DOUBLE) then
+               call endrun(subname//': Snapshot file has non-FLOAT64 data '//  &
+                    '(variable '//trim(fieldname)//'). '//                     &
+                    'This will cause answer differences! '//                    &
+                    'Please rerun CAM with ndens = 1 to write 64-bit float '// &
+                    'snapshots for use with CAM-SIMA.')
+            end if
+         end if
          ! Find the variable dimension info
          dimnames = ''
          dimids = -1
diff --git a/src/physics/utils/phys_comp.F90 b/src/physics/utils/phys_comp.F90
index 471ee9e0..4db7c9c7 100644
--- a/src/physics/utils/phys_comp.F90
+++ b/src/physics/utils/phys_comp.F90
@@ -22,11 +22,14 @@ module phys_comp
    ! suite_name: Suite we are running
    character(len=SHR_KIND_CS), public, protected :: phys_suite_name = unset_str
 
+   ! ncdata_check: Path to file for physics_check_data to verify against
+   ! at the end of every timestep (if not unset)
+   character(len=SHR_KIND_CL), public, protected :: ncdata_check = unset_str
+
    ! Private module data
    character(len=SHR_KIND_CS), allocatable :: suite_names(:)
    character(len=SHR_KIND_CS) :: suite_parts_expect(2) = (/"physics_before_coupler", "physics_after_coupler "/)
    character(len=SHR_KIND_CS), allocatable :: suite_parts(:)
-   character(len=SHR_KIND_CL)              :: ncdata_check = unset_str
    logical                                 :: ncdata_check_err = .false.
    character(len=SHR_KIND_CL)              :: cam_physics_mesh = unset_str
    character(len=SHR_KIND_CS)              :: cam_take_snapshot_before = unset_str