diff --git a/Inst_eddies/Tests/test_mean_speed.f90 b/Inst_eddies/Tests/test_mean_speed.f90
index 28486746294d4b6e7bf2703fd3115bc48a57d657..53a6573fe2fb8a434141514ddaa655ab02e12ec1 100644
--- a/Inst_eddies/Tests/test_mean_speed.f90
+++ b/Inst_eddies/Tests/test_mean_speed.f90
@@ -3,12 +3,12 @@ program test_mean_speed
   ! Libraries:
   use contour_531, only: convert_to_ind
   use gpc_f, only: shp_read_pol, polygon
-  use jumble, only: get_command_arg_dyn, deg_to_rad, twopi, rad_to_deg
+  use jumble, only: get_command_arg_dyn, deg_to_rad, twopi, rad_to_deg, assert
   use shapelib, only: shpclose, shpfileobject
   use shapelib_03, only: shp_open_03
 
   use config_m, only: config
-  use input_ssh_m, only: input_ssh, corner_whole, step, nlon
+  use input_ssh_m, only: input_ssh, corner_whole, step, nlon, uniform_lon_lat
   use mean_speed_m, only: mean_speed
 
   implicit none
@@ -37,6 +37,8 @@ program test_mean_speed
   call get_command_arg_dyn(1, ssh_fname, "Required arguments: h-file uv-file")
   call get_command_arg_dyn(2, uv_fname, "Required arguments: h-file uv-file")
   call input_ssh(periodic, ssh, u, v, ssh_fname, uv_fname, uv_fname)
+  call assert(uniform_lon_lat, &
+       "test_mean_speed only works for uniform lon_lat grid")
   write(unit = *, nml = main_nml)
   print *, "Enter namelist main_nml."
   read(unit = *, nml = main_nml)