diff --git a/src/smriprep/data/io_spec.json b/src/smriprep/data/io_spec.json
index 057c8f634f7..89238d72616 100644
--- a/src/smriprep/data/io_spec.json
+++ b/src/smriprep/data/io_spec.json
@@ -134,7 +134,7 @@
       "sphere_reg": {
         "datatype": "anat",
         "hemi": ["L", "R"],
-        "space": null,
+        "space": [null, "fsaverage"],
         "desc": "reg",
         "suffix": "sphere",
         "extension": ".surf.gii"
diff --git a/src/smriprep/utils/bids.py b/src/smriprep/utils/bids.py
index fc67828bf26..6b6f862dc40 100644
--- a/src/smriprep/utils/bids.py
+++ b/src/smriprep/utils/bids.py
@@ -22,6 +22,7 @@
 #
 """Utilities to handle BIDS inputs."""
 
+import logging
 from json import loads
 from pathlib import Path
 
@@ -30,6 +31,8 @@
 
 import smriprep
 
+LOGGER = logging.getLogger('nipype.workflow')
+
 
 def collect_derivatives(
     derivatives_dir,
@@ -92,6 +95,17 @@ def collect_derivatives(
         if not item or len(item) != 2:
             continue
 
+        # sphere_reg added ``space-fsaverage`` in sMRIPrep 0.16.0
+        if key == 'sphere_reg':
+            legacy = [f for f in item if 'space' not in layout.parse_file_entities(f)]
+            if legacy:
+                LOGGER.warning(
+                    f"Found legacy {key} derivative(s) that lack a 'space' entity; this "
+                    'naming is deprecated and may not be recognized in a future release. '
+                    'Rename or regenerate these derivatives with sMRIPrep >= 0.16.0. Files: %s',
+                    ', '.join(sorted(Path(f).name for f in legacy)),
+                )
+
         derivs_cache[key] = sorted(item)
 
     for key, qry in spec['masks'].items():
diff --git a/test/utils/derivatives.yml b/test/utils/derivatives.yml
index 35330385abf..ccd79972fe4 100644
--- a/test/utils/derivatives.yml
+++ b/test/utils/derivatives.yml
@@ -61,10 +61,12 @@ dataset_description:
     extension: .surf.gii
   - suffix: sphere
     hemi: L
+    space: fsaverage
     desc: reg
     extension: .surf.gii
   - suffix: sphere
     hemi: R
+    space: fsaverage
     desc: reg
     extension: .surf.gii
   - suffix: sphere
diff --git a/test/utils/test_bids.py b/test/utils/test_bids.py
index 75a257a598f..10207f95f92 100644
--- a/test/utils/test_bids.py
+++ b/test/utils/test_bids.py
@@ -20,6 +20,8 @@
 #
 #     https://www.nipreps.org/community/licensing/
 #
+import logging
+
 import pytest
 from niworkflows.utils.testing import generate_bids_skeleton
 
@@ -59,6 +61,40 @@ def test_collect_derivatives(deriv_dset):
         assert len(collected[surface]) == 2
 
 
+@pytest.mark.parametrize(
+    ('sphere_reg_entities', 'warns'),
+    [
+        pytest.param({'desc': 'reg'}, True, id='without-fsaverage'),
+        pytest.param({'space': 'fsaverage', 'desc': 'reg'}, False, id='with-fsaverage'),
+    ],
+)
+def test_collect_derivatives_reuses_sphere_reg(tmp_path, caplog, sphere_reg_entities, warns):
+    """The fsaverage registration sphere is reusable under both naming conventions."""
+    skeleton = {
+        '01': [
+            {
+                'anat': [
+                    {
+                        'suffix': 'sphere',
+                        'hemi': hemi,
+                        'extension': '.surf.gii',
+                        **sphere_reg_entities,
+                    }
+                    for hemi in ('L', 'R')
+                ]
+            }
+        ]
+    }
+    deriv_dir = tmp_path / 'derivatives'
+    generate_bids_skeleton(deriv_dir, skeleton)
+
+    with caplog.at_level(logging.WARNING, logger='nipype.workflow'):
+        collected = collect_derivatives(deriv_dir, '01', [])
+
+    assert len(collected['sphere_reg']) == 2
+    assert any('legacy sphere_reg' in record.message for record in caplog.records) is warns
+
+
 def test_collect_derivatives_transforms(deriv_dset):
     """Ensure transforms are collected for the right spaces."""
     output_spaces = ['MNI152NLin2009cAsym', 'MNIPediatricAsym:cohort-3']