diff --git a/tests/test_coastal_vulnerability.py b/tests/test_coastal_vulnerability.py
index 9f3f7b51d2..8d8a6a37d2 100644
--- a/tests/test_coastal_vulnerability.py
+++ b/tests/test_coastal_vulnerability.py
@@ -224,27 +224,29 @@ def test_extract_bathymetry(self):
         projection_wkt = srs.ExportToWkt()
         geotransform = [0, 1.0, 0.0, 0, 0.0, -1.0]
         n = 5
-        nodata_val = 9999
+        band1_nodata = numpy.nan
         gtiff_driver = gdal.GetDriverByName('GTiff')
         new_raster = gtiff_driver.Create(
-            raster_path, n, n, 2, gdal.GDT_Int32, options=[
+            raster_path, n, n, 2, gdal.GDT_Float32, options=[
                 'TILED=YES', 'BIGTIFF=YES', 'COMPRESS=LZW',
                 'BLOCKXSIZE=16', 'BLOCKYSIZE=16'])
         new_raster.SetProjection(projection_wkt)
         new_raster.SetGeoTransform(geotransform)
-        array = numpy.array([-1]*n*n).reshape((n, n))
+        valid_value = -10.0
+        array = numpy.array([valid_value]*n*n).reshape((n, n))
 
         # nodata across the top row for Band 1
         new_band = new_raster.GetRasterBand(1)
-        array[:1] = nodata_val
+        array[:1] = band1_nodata
         new_band.WriteArray(array)
-        new_band.SetNoDataValue(nodata_val)
+        new_band.SetNoDataValue(band1_nodata)
 
         # all nodata for Band 2
+        band2_nodata = 999.99
         nodata_band = new_raster.GetRasterBand(2)
-        array[:] = nodata_val
+        array[:] = band2_nodata
         nodata_band.WriteArray(array)
-        nodata_band.SetNoDataValue(nodata_val)
+        nodata_band.SetNoDataValue(band2_nodata)
 
         new_raster.FlushCache()
         new_band = None
@@ -276,25 +278,25 @@ def test_extract_bathymetry(self):
         band = raster.GetRasterBand(1)  # nodata across top row
 
         values = coastal_vulnerability.extract_bathymetry_along_ray(
-            all_valid_ray, geotransform, nodata_val, band)
-        self.assertTrue(numpy.mean(values) == -1)
+            all_valid_ray, geotransform, band1_nodata, band)
+        self.assertEqual(numpy.mean(values), valid_value)
 
         values = coastal_vulnerability.extract_bathymetry_along_ray(
-            some_nodata_ray, geotransform, nodata_val, band)
-        self.assertTrue(numpy.mean(values) == -1)
+            some_nodata_ray, geotransform, band1_nodata, band)
+        self.assertEqual(numpy.mean(values), valid_value)
 
         values = coastal_vulnerability.extract_bathymetry_along_ray(
-            all_nodata_ray, geotransform, nodata_val, band)
-        self.assertTrue(numpy.mean(values) == -1)
+            all_nodata_ray, geotransform, band1_nodata, band)
+        self.assertEqual(numpy.mean(values), valid_value)
 
         with self.assertRaises(ValueError):
             values = coastal_vulnerability.extract_bathymetry_along_ray(
-                out_of_bounds_ray, geotransform, nodata_val, band)
+                out_of_bounds_ray, geotransform, band1_nodata, band)
 
         nodata_band = raster.GetRasterBand(2)  # all nodata band
         with self.assertRaises(ValueError):
             values = coastal_vulnerability.extract_bathymetry_along_ray(
-                all_valid_ray, geotransform, nodata_val, nodata_band)
+                all_valid_ray, geotransform, band2_nodata, nodata_band)
 
         raster = None
         band = None