diff --git a/src/bids_validator/bids_validator.py b/src/bids_validator/bids_validator.py
index 6c25ab5..261537f 100644
--- a/src/bids_validator/bids_validator.py
+++ b/src/bids_validator/bids_validator.py
@@ -103,7 +103,11 @@ def _init_regexes(cls) -> None:
 
             all_rules = chain.from_iterable(
                 bst.rules.regexify_filename_rules(group, schema, level=2)
-                for group in (schema.rules.files.common, schema.rules.files.raw)
+                for group in (
+                    schema.rules.files.common,
+                    schema.rules.files.raw,
+                    schema.rules.files.deriv,
+                )
             )
             cls.regexes = [rule['regex'] for rule in all_rules]
 
diff --git a/tests/test_derivatives.py b/tests/test_derivatives.py
new file mode 100644
index 0000000..12082a3
--- /dev/null
+++ b/tests/test_derivatives.py
@@ -0,0 +1,56 @@
+"""Test BIDSValidator support for derivative filenames."""
+
+import pytest
+
+from bids_validator import BIDSValidator
+
+
+@pytest.mark.parametrize(
+    'fname',
+    [
+        '/sub-04/anat/sub-04_space-MNI152_T1w.nii.gz',  # space
+        '/sub-04/anat/sub-04_space-MNI152_desc-preproc_T1w.nii.gz',  # space + desc
+        '/sub-04/ses-02/func/sub-04_ses-02_task-rest_space-MNI152NLin2009cAsym_desc-preproc_bold.nii',  # space + desc
+        '/sub-04/ses-02/func/sub-04_ses-02_task-nback_run-02_space-T1w_label-brain_mask.nii',  # space + label
+        '/sub-04/ses-01/func/sub-04_ses-01_task-nback_run-01_space-T1w_desc-preproc_bold.json',  # space + desc
+        '/sub-01/anat/sub-01_res-1_T1w.nii.gz',  # res
+        '/sub-01/anat/sub-01_space-MNI152_dseg.nii.gz',  # dseg suffix
+    ],
+)
+def test_derivative_filenames_are_bids(fname: str) -> None:
+    """Test that derivative filenames are recognized as valid BIDS."""
+    assert BIDSValidator.is_bids(fname)
+
+
+@pytest.mark.parametrize(
+    ('fname', 'expected'),
+    [
+        (
+            '/sub-04/anat/sub-04_space-MNI152_desc-preproc_T1w.nii.gz',
+            {
+                'subject': '04',
+                'datatype': 'anat',
+                'space': 'MNI152',
+                'description': 'preproc',
+                'suffix': 'T1w',
+                'extension': '.nii.gz',
+            },
+        ),
+        (
+            '/sub-04/ses-02/func/sub-04_ses-02_task-rest_space-MNI152NLin2009cAsym_desc-preproc_bold.nii',
+            {
+                'subject': '04',
+                'session': '02',
+                'datatype': 'func',
+                'task': 'rest',
+                'space': 'MNI152NLin2009cAsym',
+                'description': 'preproc',
+                'suffix': 'bold',
+                'extension': '.nii',
+            },
+        ),
+    ],
+)
+def test_parse_derivative_entities(fname: str, expected: dict[str, str]) -> None:
+    """Test that parse() returns derivative-specific entities."""
+    assert BIDSValidator.parse(fname) == expected