diff --git a/mne_bids/tests/test_dig.py b/mne_bids/tests/test_dig.py
index f5b7168eb..a80147ec1 100644
--- a/mne_bids/tests/test_dig.py
+++ b/mne_bids/tests/test_dig.py
@@ -142,20 +142,22 @@ def test_dig_template(tmp_path):
     for datatype in ("eeg", "ieeg"):
         (bids_root / "sub-01" / "ses-01" / datatype).mkdir(parents=True)
 
+    raw = _load_raw()
+    raw.pick(["eeg"])
+    montage = raw.get_montage()
+
     for datatype in ("eeg", "ieeg"):
         bids_path = _bids_path.copy().update(root=bids_root, datatype=datatype)
         for coord_frame in BIDS_STANDARD_TEMPLATE_COORDINATE_SYSTEMS:
-            raw = _load_raw()
-            raw.pick(["eeg"])
             bids_path.update(space=coord_frame)
-            montage = raw.get_montage()
-            pos = montage.get_positions()
+            _montage = montage.copy()
+            pos = _montage.get_positions()
             mne_coord_frame = BIDS_TO_MNE_FRAMES.get(coord_frame, None)
             if mne_coord_frame is None:
-                montage.apply_trans(mne.transforms.Transform("head", "unknown"))
+                _montage.apply_trans(mne.transforms.Transform("head", "unknown"))
             else:
-                montage.apply_trans(mne.transforms.Transform("head", mne_coord_frame))
-            _write_dig_bids(bids_path, raw, montage, acpc_aligned=True)
+                _montage.apply_trans(mne.transforms.Transform("head", mne_coord_frame))
+            _write_dig_bids(bids_path, raw, _montage, acpc_aligned=True)
             electrodes_path = bids_path.copy().update(
                 task=None, run=None, suffix="electrodes", extension=".tsv"
             )