diff --git a/xarray/core/dataset.py b/xarray/core/dataset.py
index 30cba39d249..0df81999728 100644
--- a/xarray/core/dataset.py
+++ b/xarray/core/dataset.py
@@ -3832,7 +3832,12 @@ def unstack(
 
         result = self.copy(deep=False)
         for dim in dims:
-            if sparse:
+            # FIXME: remove
+            import sparse as sparse_
+
+            if sparse or any(
+                isinstance(v.data, sparse_.COO) for v in self.variables.values()
+            ):
                 result = result._unstack_once(dim, fill_value, sparse)
             else:
                 result = result._unstack_once_fast(dim, fill_value, sparse)
diff --git a/xarray/core/variable.py b/xarray/core/variable.py
index b75def6d509..ec43c3b0ab5 100644
--- a/xarray/core/variable.py
+++ b/xarray/core/variable.py
@@ -1597,8 +1597,6 @@ def _unstack_once_fast(
         new_shape = list(reordered.shape[: len(other_dims)]) + new_dim_sizes
         new_dims = reordered.dims[: len(other_dims)] + new_dim_names
 
-        # missing_values = np.prod(new_shape) > np.prod(self.shape)
-
         if fill_value is dtypes.NA:
             fill_value = dtypes.get_fill_value(self.dtype)