diff --git a/nipype/interfaces/spm/preprocess.py b/nipype/interfaces/spm/preprocess.py
index 505016b7a7..8db09b2bfb 100644
--- a/nipype/interfaces/spm/preprocess.py
+++ b/nipype/interfaces/spm/preprocess.py
@@ -1491,7 +1491,10 @@ def _list_outputs(self):
                 filelist = ensure_list(self.inputs.apply_to_files)
                 for f in filelist:
                     if isinstance(f, list):
-                        run = [fname_presuffix(in_f, prefix=self.inputs.out_prefix) for in_f in f]
+                        run = [
+                            fname_presuffix(in_f, prefix=self.inputs.out_prefix)
+                            for in_f in f
+                        ]
                     else:
                         run = [fname_presuffix(f, prefix=self.inputs.out_prefix)]
                     outputs["normalized_files"].extend(run)