diff --git a/holoviews/core/data/__init__.py b/holoviews/core/data/__init__.py
index f266adbe45..977da78443 100644
--- a/holoviews/core/data/__init__.py
+++ b/holoviews/core/data/__init__.py
@@ -359,7 +359,8 @@ def aggregate(self, dimensions=None, function=None, spreadfn=None, **kwargs):
             combined = self.clone(aggregated, kdims=kdims)
             for i, d in enumerate(vdims):
                 dim = d('_'.join([d.name, spread_name]))
-                combined = combined.add_dimension(dim, ndims+i, error[d], True)
+                dvals = error.dimension_values(d, False, False)
+                combined = combined.add_dimension(dim, ndims+i, dvals, True)
             return combined
 
         if np.isscalar(aggregated):
diff --git a/holoviews/core/data/xarray.py b/holoviews/core/data/xarray.py
index a10ce1f930..557cc7ff13 100644
--- a/holoviews/core/data/xarray.py
+++ b/holoviews/core/data/xarray.py
@@ -194,7 +194,8 @@ def select(cls, dataset, selection_mask=None, **selection):
             if isinstance(v, set):
                 validated[k] = list(v)
             elif isinstance(v, tuple):
-                validated[k] = slice(v[0], v[1]-sys.float_info.epsilon*10)
+                upper = None if v[1] is None else v[1]-sys.float_info.epsilon*10
+                validated[k] = slice(v[0], upper)
             elif isinstance(v, types.FunctionType):
                 validated[k] = v(dataset[k])
             else:
@@ -234,7 +235,9 @@ def add_dimension(cls, dataset, dimension, dim_pos, values, vdim):
         if not vdim:
             raise Exception("Cannot add key dimension to a dense representation.")
         dim = dimension.name if isinstance(dimension, Dimension) else dimension
-        return dataset.assign(**{dim: values})
+        arr = xr.DataArray(values, coords=dataset.data.coords, name=dim,
+                           dims=dataset.data.dims)
+        return dataset.data.assign(**{dim: arr})
 
 
 Interface.register(XArrayInterface)