diff --git a/pyproject.toml b/pyproject.toml
index 37ab4b2241..aaef895ccf 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -193,7 +193,6 @@ ignore = [
   "B019",
   "SIM108",
   "C901",
-  "UP038",
 ]
 
 [tool.ruff.lint.flake8-quotes]
diff --git a/sdcflows/workflows/base.py b/sdcflows/workflows/base.py
index 88c5afd267..40f938b6a6 100644
--- a/sdcflows/workflows/base.py
+++ b/sdcflows/workflows/base.py
@@ -137,6 +137,7 @@ def init_fmap_preproc_wf(
         fmap_derivatives_wf = init_fmap_derivatives_wf(
             output_dir=str(output_dir),
             write_coeff=True,
+            write_mask=True,
             bids_fmap_id=estimator.bids_id,
             name=f'fmap_derivatives_wf_{estimator.sanitized_id}',
         )
@@ -157,18 +158,16 @@ def init_fmap_preproc_wf(
                 niu.IdentityInterface(fields=fields),
                 name=f'in_{estimator.sanitized_id}',
             )
-            # fmt:off
             workflow.connect([
                 (inputnode, est_wf, [(f, f"inputnode.{f}") for f in fields])
-            ])
-            # fmt:on
+            ])  # fmt:skip
 
-        # fmt:off
         workflow.connect([
             (est_wf, fmap_derivatives_wf, [
                 ("outputnode.fmap", "inputnode.fieldmap"),
                 ("outputnode.fmap_ref", "inputnode.fmap_ref"),
                 ("outputnode.fmap_coeff", "inputnode.fmap_coeff"),
+                ("outputnode.fmap_mask", "inputnode.fmap_mask"),
             ]),
             (est_wf, fmap_reports_wf, [
                 ("outputnode.fmap", "inputnode.fieldmap"),
@@ -176,14 +175,15 @@ def init_fmap_preproc_wf(
                 ("outputnode.fmap_mask", "inputnode.fmap_mask"),
             ]),
             (est_wf, out_map, [
-                ("outputnode.fmap", "fmap"),
+                ("outputnode.method", "method")
+            ]),
+            (fmap_derivatives_wf, out_map, [
+                ("outputnode.fieldmap", "fmap"),
                 ("outputnode.fmap_ref", "fmap_ref"),
                 ("outputnode.fmap_coeff", "fmap_coeff"),
                 ("outputnode.fmap_mask", "fmap_mask"),
-                ("outputnode.method", "method")
             ]),
-        ])
-        # fmt:on
+        ])  # fmt:skip
 
         for field, mergenode in out_merge.items():
             workflow.connect(out_map, field, mergenode, f'in{n}')
diff --git a/sdcflows/workflows/outputs.py b/sdcflows/workflows/outputs.py
index ce5aa09997..a7913d4a0c 100644
--- a/sdcflows/workflows/outputs.py
+++ b/sdcflows/workflows/outputs.py
@@ -98,14 +98,12 @@ def init_fmap_reports_wf(
             suffix='fieldmap',
             desc=fmap_type,
             dismiss_entities=('fmap',),
-            allowed_entities=tuple(custom_entities.keys()),
+            allowed_entities=tuple(custom_entities),
         ),
         name='ds_fmap_report',
     )
-    for k, v in custom_entities.items():
-        setattr(ds_fmap_report.inputs, k, v)
+    ds_fmap_report.inputs.trait_set(**custom_entities)
 
-    # fmt:off
     workflow.connect([
         (inputnode, fmap_rpt, [(("fieldmap", _pop), "fieldmap"),
                                ("fmap_ref", "reference"),
@@ -113,8 +111,7 @@ def init_fmap_reports_wf(
         (fmap_rpt, ds_fmap_report, [("out_report", "in_file")]),
         (inputnode, ds_fmap_report, [("source_files", "source_file")]),
 
-    ])
-    # fmt:on
+    ])  # fmt:skip
 
     return workflow
 
@@ -126,6 +123,7 @@ def init_fmap_derivatives_wf(
     custom_entities=None,
     name='fmap_derivatives_wf',
     write_coeff=False,
+    write_mask=False,
 ):
     """
     Set up datasinks to store derivatives in the right location.
@@ -162,10 +160,14 @@ def init_fmap_derivatives_wf(
     workflow = pe.Workflow(name=name)
     inputnode = pe.Node(
         niu.IdentityInterface(
-            fields=['source_files', 'fieldmap', 'fmap_coeff', 'fmap_ref', 'fmap_meta']
+            fields=['source_files', 'fieldmap', 'fmap_coeff', 'fmap_ref', 'fmap_mask', 'fmap_meta']
         ),
         name='inputnode',
     )
+    outputnode = pe.Node(
+        niu.IdentityInterface(fields=['fieldmap', 'fmap_coeff', 'fmap_ref', 'fmap_mask']),
+        name='outputnode',
+    )
 
     merge_fmap = pe.Node(MergeSeries(), name='merge_fmap')
 
@@ -176,7 +178,7 @@ def init_fmap_derivatives_wf(
             suffix='fieldmap',
             datatype='fmap',
             dismiss_entities=('fmap',),
-            allowed_entities=tuple(custom_entities.keys()),
+            allowed_entities=tuple(custom_entities),
         ),
         name='ds_reference',
     )
@@ -188,7 +190,7 @@ def init_fmap_derivatives_wf(
             suffix='fieldmap',
             datatype='fmap',
             compress=True,
-            allowed_entities=tuple(custom_entities.keys()),
+            allowed_entities=tuple(custom_entities),
         ),
         name='ds_fieldmap',
     )
@@ -196,11 +198,9 @@ def init_fmap_derivatives_wf(
     if bids_fmap_id:
         ds_fieldmap.inputs.B0FieldIdentifier = bids_fmap_id
 
-    for k, v in custom_entities.items():
-        setattr(ds_reference.inputs, k, v)
-        setattr(ds_fieldmap.inputs, k, v)
+    ds_reference.inputs.trait_set(**custom_entities)
+    ds_fieldmap.inputs.trait_set(**custom_entities)
 
-    # fmt:off
     workflow.connect([
         (inputnode, merge_fmap, [("fieldmap", "in_files")]),
         (inputnode, ds_reference, [("source_files", "source_file"),
@@ -213,8 +213,38 @@ def init_fmap_derivatives_wf(
             (("out_file", _getname), "AnatomicalReference"),
         ]),
         (inputnode, ds_fieldmap, [(("fmap_meta", _selectintent), "IntendedFor")]),
-    ])
-    # fmt:on
+        (ds_fieldmap, outputnode, [("out_file", "fieldmap")]),
+        (ds_reference, outputnode, [("out_file", "fmap_ref")]),
+    ])  # fmt:skip
+
+    if write_mask:
+        ds_mask = pe.Node(
+            DerivativesDataSink(
+                base_directory=output_dir,
+                compress=True,
+                desc='brain',
+                suffix='mask',
+                datatype='fmap',
+                dismiss_entities=('fmap',),
+                allowed_entities=tuple(custom_entities),
+            ),
+            name='ds_mask',
+        )
+        ds_mask._interface._file_patterns += (
+            'sub-{subject}[/ses-{session}]/{datatype<fmap>|fmap}/'
+            'sub-{subject}[_ses-{session}][_hash-{hash}][_acq-{acquisition}]'
+            '[_dir-{direction}][_run-{run}][_part-{part}][_space-{space}]'
+            '[_cohort-{cohort}][_res-{resolution}][_fmapid-{fmapid}]'
+            '[_desc-{desc}]_{suffix<mask>}{extension<.nii|.nii.gz|.json>|.nii.gz}',
+        )
+
+        ds_mask.inputs.trait_set(**custom_entities)
+
+        workflow.connect([
+            (inputnode, ds_mask, [("source_files", "source_file"),
+                                  ("fmap_mask", "in_file")]),
+            (ds_mask, outputnode, [("out_file", "fmap_mask")]),
+        ])  # fmt:skip
 
     if not write_coeff:
         return workflow
@@ -225,7 +255,7 @@ def init_fmap_derivatives_wf(
             suffix='fieldmap',
             datatype='fmap',
             compress=True,
-            allowed_entities=tuple(custom_entities.keys()),
+            allowed_entities=tuple(custom_entities),
         ),
         name='ds_coeff',
         iterfield=('in_file', 'desc'),
@@ -233,18 +263,16 @@ def init_fmap_derivatives_wf(
 
     gen_desc = pe.Node(niu.Function(function=_gendesc), name='gen_desc')
 
-    for k, v in custom_entities.items():
-        setattr(ds_coeff.inputs, k, v)
+    ds_coeff.inputs.trait_set(**custom_entities)
 
-    # fmt:off
     workflow.connect([
         (inputnode, ds_coeff, [("source_files", "source_file"),
                                ("fmap_coeff", "in_file")]),
         (inputnode, gen_desc, [("fmap_coeff", "infiles")]),
         (gen_desc, ds_coeff, [("out", "desc")]),
         (ds_coeff, ds_fieldmap, [(("out_file", _getname), "AssociatedCoefficients")]),
-    ])
-    # fmt:on
+        (ds_coeff, outputnode, [("out_file", "fmap_coeff")]),
+    ])  # fmt:skip
 
     return workflow