diff --git a/sdcflows/workflows/base.py b/sdcflows/workflows/base.py
index a988a78862..0208c3fdbf 100644
--- a/sdcflows/workflows/base.py
+++ b/sdcflows/workflows/base.py
@@ -70,15 +70,25 @@ def init_fmap_preproc_wf(
     from .outputs import init_fmap_derivatives_wf, init_fmap_reports_wf
 
     workflow = Workflow(name=name)
-    for estimator in estimators:
+
+    out_fields = ("fmap", "fmap_ref", "fmap_coeff", "fmap_mask")
+    out_merge = {
+        f: pe.Node(niu.Merge(len(estimators)), name=f"out_merge_{f}")
+        for f in out_fields
+    }
+    outputnode = pe.Node(niu.IdentityInterface(fields=out_fields), name="outputnode")
+
+    workflow.connect([
+        (mergenode, outputnode, [("out", field)])
+        for field, mergenode in out_merge.items()
+    ])
+
+    for n, estimator in enumerate(estimators):
         est_wf = estimator.get_workflow(omp_nthreads=omp_nthreads, debug=debug)
         source_files = [str(f.path) for f in estimator.sources]
 
-        outputnode = pe.Node(
-            niu.IdentityInterface(
-                fields=["fmap", "fmap_ref", "fmap_coeff", "fmap_mask"]
-            ),
-            name=f"out_{estimator.bids_id}",
+        out_map = pe.Node(
+            niu.IdentityInterface(fields=out_fields), name=f"out_{estimator.bids_id}"
         )
 
         fmap_derivatives_wf = init_fmap_derivatives_wf(
@@ -116,7 +126,7 @@ def init_fmap_preproc_wf(
                 (est_wf, fmap_reports_wf, [
                     ("outputnode.fmap_mask", "inputnode.fmap_mask"),
                 ]),
-                (est_wf, outputnode, [("outputnode.fmap_mask", "fmap_mask")]),
+                (est_wf, out_map, [("outputnode.fmap_mask", "fmap_mask")]),
             ])
             # fmt:on
 
@@ -131,11 +141,15 @@ def init_fmap_preproc_wf(
                 ("outputnode.fmap", "inputnode.fieldmap"),
                 ("outputnode.fmap_ref", "inputnode.fmap_ref"),
             ]),
-            (est_wf, outputnode, [
+            (est_wf, out_map, [
                 ("outputnode.fmap", "fmap"),
                 ("outputnode.fmap_ref", "fmap_ref"),
                 ("outputnode.fmap_coeff", "fmap_coeff"),
             ]),
         ])
         # fmt:on
+
+        for field, mergenode in out_merge.items():
+            workflow.connect(out_map, field, mergenode, f"in{n}")
+
     return workflow