diff --git a/sup3r/preprocessing/accessor.py b/sup3r/preprocessing/accessor.py
index 50b9dfb73..598bdeac1 100644
--- a/sup3r/preprocessing/accessor.py
+++ b/sup3r/preprocessing/accessor.py
@@ -19,7 +19,6 @@
     compute_if_dask,
     dims_array_tuple,
     is_type_of,
-    lower_names,
     ordered_array,
     ordered_dims,
     parse_keys,
@@ -90,7 +89,7 @@ def __init__(self, ds: Union[xr.Dataset, Self]):
         ds : xr.Dataset | xr.DataArray
             xarray Dataset instance to access with the following methods
         """
-        self._ds = lower_names(ds)
+        self._ds = ds
         self._features = None
         self._meta = None
         self.time_slice = None
diff --git a/sup3r/preprocessing/utilities.py b/sup3r/preprocessing/utilities.py
index 2f650a71c..8a51fadbf 100644
--- a/sup3r/preprocessing/utilities.py
+++ b/sup3r/preprocessing/utilities.py
@@ -23,17 +23,16 @@
 
 def lower_names(data):
     """Set all fields / coords / dims to lower case."""
-    return data.rename(
-        {
-            f: f.lower()
-            for f in [
-                *list(data.data_vars),
-                *list(data.dims),
-                *list(data.coords),
-            ]
-            if f != f.lower()
-        }
-    )
+    rename_map = {
+        f: f.lower()
+        for f in [
+            *list(data.data_vars),
+            *list(data.dims),
+            *list(data.coords),
+        ]
+        if f != f.lower()
+    }
+    return data.rename(rename_map)
 
 
 def get_input_handler_class(input_handler_name: Optional[str] = None):