diff --git a/clinica/iotools/bids_utils.py b/clinica/iotools/bids_utils.py
index 19ec84547..324ef4571 100644
--- a/clinica/iotools/bids_utils.py
+++ b/clinica/iotools/bids_utils.py
@@ -292,7 +292,7 @@ def from_original_study_id(cls, study_id: str) -> str:
         )
 
     def to_original_study_id(self) -> str:
-        return str(self.replace("sub-HABS", "P_"))
+        return str(self).replace("sub-HABS", "P_")
 
 
 class IXIBIDSSubjectID(BIDSSubjectID):
@@ -317,7 +317,7 @@ def from_original_study_id(cls, study_id: str) -> str:
         )
 
     def to_original_study_id(self) -> str:
-        return str(self.replace("sub-", ""))
+        return str(self).replace("sub-", "")
 
 
 # -- Methods for the clinical data --
diff --git a/test/unittests/iotools/test_bids_utils.py b/test/unittests/iotools/test_bids_utils.py
index f39bdef63..a26dbe03b 100644
--- a/test/unittests/iotools/test_bids_utils.py
+++ b/test/unittests/iotools/test_bids_utils.py
@@ -93,7 +93,7 @@ def test_study_to_bids_id_value_error(study, study_id):
 
 
 @pytest.mark.parametrize(
-    "study,expected,bids_id",
+    "study,source_id,bids_id",
     [
         (StudyName.ADNI, "001_S_0001", "sub-ADNI001S0001"),
         (StudyName.NIFD, "1_S_0001", "sub-NIFD1S0001"),
@@ -106,10 +106,10 @@ def test_study_to_bids_id_value_error(study, study_id):
         (StudyName.IXI, "IXI001", "sub-IXI001"),
     ],
 )
-def test_bids_to_study(study, bids_id, expected):
+def test_bids_to_study(study, bids_id, source_id):
     from clinica.iotools.bids_utils import bids_id_factory
 
-    assert bids_id_factory(study).to_original_study_id(bids_id) == expected
+    assert bids_id_factory(study)(bids_id).to_original_study_id() == source_id
 
 
 def create_clinical_data(tmp_path: Path, study_name: StudyName) -> Path: