diff --git a/ow_calibration/get_region/get_region_hist_locations.py b/ow_calibration/get_region/get_region_hist_locations.py
index c4893275..6aa4a12f 100644
--- a/ow_calibration/get_region/get_region_hist_locations.py
+++ b/ow_calibration/get_region/get_region_hist_locations.py
@@ -25,6 +25,7 @@
 from ow_calibration.get_region.data_functions.get_data import get_data
 from ow_calibration.get_region.data_functions.wrap_longitude import wrap_longitude
 
+
 # pylint: disable=bare-except
 def get_region_hist_locations(pa_wmo_numbers, pa_float_name, config):
     """
@@ -66,14 +67,13 @@ def get_region_hist_locations(pa_wmo_numbers, pa_float_name, config):
 
     if grid_lat.__len__() == 0:
 
-        grid_lat = 999
-        grid_long = 999
-        grid_dates = 'NaN'
+        raise ValueError("get_region_hist_locations found no data for your specification. "
+                         "Are your wmo_boxes files set up correctly?")
+
 
-    else:
 
-        grid_long = wrap_longitude(grid_long)
-        # decimalise dates
-        grid_dates = change_dates(grid_dates)
+    grid_long = wrap_longitude(grid_long)
+    # decimalise dates
+    grid_dates = change_dates(grid_dates)
 
     return grid_lat, grid_long, grid_dates
diff --git a/ow_calibration/get_region/get_region_hist_locations_test.py b/ow_calibration/get_region/get_region_hist_locations_test.py
index 1264a664..a7396fcf 100644
--- a/ow_calibration/get_region/get_region_hist_locations_test.py
+++ b/ow_calibration/get_region/get_region_hist_locations_test.py
@@ -84,12 +84,12 @@ def test_no_data(self):
         print("Testing that get_region_hist_locations returns expected values for no data")
 
         wmo_boxes_no_data = np.array([[3505, 0, 0, 0]])
-        lat_no_data, long_no_data, age_no_data = get_region_hist_locations(wmo_boxes_no_data,
-                                                                           'none',
-                                                                           self.config)
 
-        self.assertEqual(lat_no_data, long_no_data, "latitude and longitude should be equal (999)")
-        self.assertEqual(age_no_data, 'NaN', "age should be NaN")
+        with self.assertRaises(ValueError) as no_data:
+            get_region_hist_locations(wmo_boxes_no_data, 'none', self.config)
+
+        self.assertTrue('get_region_hist_locations found no data for your specification. '
+                        'Are your wmo_boxes files set up correctly?' in str(no_data.exception))
 
     def test_can_choose_data(self):
         """