diff --git a/xbout/tests/test_boutdataset.py b/xbout/tests/test_boutdataset.py
index a03c4ed9..61c03d11 100644
--- a/xbout/tests/test_boutdataset.py
+++ b/xbout/tests/test_boutdataset.py
@@ -1195,10 +1195,14 @@ def test_integrate_midpoints_slab(self, bout_xyt_example_files):
         x = np.linspace(0.05, 9.95, 100)[np.newaxis, :, np.newaxis, np.newaxis]
         y = np.linspace(0.1, 21.9, 110)[np.newaxis, np.newaxis, :, np.newaxis]
         z = np.linspace(0.15, 35.85, 120)[np.newaxis, np.newaxis, np.newaxis, :]
-        ds["t"].data[...] = t.squeeze()
-        ds["dx"].data[...] = 0.1
-        ds["dy"].data[...] = 0.2
-        ds["dz"] = 0.3
+        ds["dx"][...] = 0.1
+        ds["dy"][...] = 0.2
+        ds = ds.assign_coords(
+            t=t.squeeze(),
+            dx=ds.dx,
+            dy=ds.dy,
+            dz=0.3,
+        )
         tfunc = 1.5 * t
         xfunc = x**2
         yfunc = 10.0 * y - y**2