diff --git a/tests/test_accessor.py b/tests/test_accessor.py
new file mode 100644
index 0000000..7ec84d6
--- /dev/null
+++ b/tests/test_accessor.py
@@ -0,0 +1,17 @@
+import pytest
+import xarray as xr
+
+import xarray_subset_grid.accessor  # noqa: F401
+
+
+def test_data_vars_returns_empty_set_when_grid_not_recognized():
+    ds = xr.Dataset(
+        data_vars={"foo": ("x", [1, 2, 3])},
+        coords={"x": [0, 1, 2]},
+    )
+
+    with pytest.warns(UserWarning, match="no grid type found in this dataset"):
+        accessor = ds.xsg
+
+    assert accessor.grid is None
+    assert accessor.data_vars == set()
diff --git a/xarray_subset_grid/accessor.py b/xarray_subset_grid/accessor.py
index 7a4ca7a..1b127fd 100644
--- a/xarray_subset_grid/accessor.py
+++ b/xarray_subset_grid/accessor.py
@@ -1,4 +1,5 @@
 import warnings
+from typing import TYPE_CHECKING
 
 # from typing import Optional, Union
 import numpy as np
@@ -15,6 +16,9 @@
     UGrid,
 )
 
+if TYPE_CHECKING:
+    from xarray.core.coordinates import DatasetCoordinates
+
 _grid_impls = [
     FVCOMGrid,
     SELFEGrid,
@@ -78,15 +82,13 @@ def data_vars(self) -> set[str]:
         data analysis. These can be discarded when subsetting the
         dataset when they are not needed.
         """
-        if self._ds:
+        if self._grid:
             return self._grid.data_vars(self._ds)
         return set()
 
     @property
-    def coords(self) -> set[str]:
-        if self._ds:
-            return self._ds.coords
-        return set()
+    def coords(self) -> "DatasetCoordinates":
+        return self._ds.coords
 
     @property
     def grid_vars(self) -> set[str]: