diff --git a/swh/lister/gitlab/lister.py b/swh/lister/gitlab/lister.py
--- a/swh/lister/gitlab/lister.py
+++ b/swh/lister/gitlab/lister.py
@@ -4,6 +4,7 @@
 
 import random
 import time
+from urllib3.util import parse_url
 
 from ..core.page_by_page_lister import PageByPageHttpLister
 from .models import GitLabModel
@@ -15,10 +16,12 @@
     MODEL = GitLabModel
     LISTER_NAME = 'gitlab'
 
-    def __init__(self, api_baseurl=None, instance=None,
+    def __init__(self, api_baseurl, instance=None,
                  override_config=None, sort='asc', per_page=20):
         super().__init__(api_baseurl=api_baseurl,
                          override_config=override_config)
+        if instance is None:
+            instance = parse_url(api_baseurl).host
         self.instance = instance
         self.PATH_TEMPLATE = '%s&sort=%s' % (self.PATH_TEMPLATE, sort)
         if per_page != 20:
diff --git a/swh/lister/gitlab/tasks.py b/swh/lister/gitlab/tasks.py
--- a/swh/lister/gitlab/tasks.py
+++ b/swh/lister/gitlab/tasks.py
@@ -17,7 +17,7 @@
 
 
 def new_lister(api_baseurl='https://gitlab.com/api/v4',
-               instance='gitlab', sort='asc', per_page=20):
+               instance=None, sort='asc', per_page=20):
     return GitLabLister(
         api_baseurl=api_baseurl, instance=instance, sort=sort,
         per_page=per_page)
diff --git a/swh/lister/gitlab/tests/test_tasks.py b/swh/lister/gitlab/tests/test_tasks.py
--- a/swh/lister/gitlab/tests/test_tasks.py
+++ b/swh/lister/gitlab/tests/test_tasks.py
@@ -28,7 +28,7 @@
 
     lister.assert_called_once_with(
         api_baseurl='https://gitlab.com/api/v4',
-        instance='gitlab', sort='desc', per_page=20)
+        instance=None, sort='desc', per_page=20)
     lister.db_last_index.assert_not_called()
     lister.get_pages_information.assert_called_once_with()
     lister.run.assert_called_once_with(
@@ -50,7 +50,7 @@
 
     lister.assert_called_once_with(
         api_baseurl='https://gitlab.com/api/v4',
-        instance='gitlab', sort='asc', per_page=20)
+        instance=None, sort='asc', per_page=20)
     lister.db_last_index.assert_not_called()
     lister.run.assert_called_once_with(min_bound=12, max_bound=42)
 
@@ -83,7 +83,55 @@
 
     lister.assert_called_with(
         api_baseurl='https://gitlab.com/api/v4',
-        instance='gitlab', sort='asc', per_page=20)
+        instance=None, sort='asc', per_page=20)
+
+    # one by the FullGitlabRelister task
+    # + 9 for the RangeGitlabLister subtasks
+    assert lister.call_count == 10
+
+    lister.db_last_index.assert_not_called()
+    lister.db_partition_indices.assert_not_called()
+    lister.get_pages_information.assert_called_once_with()
+
+    # lister.run should have been called once per partition interval
+    for i in range(8):
+        # XXX inconsistent behavior: max_bound is EXCLUDED here
+        assert (dict(min_bound=10*i, max_bound=10*i + 10),) \
+            in lister.run.call_args_list
+    assert (dict(min_bound=80, max_bound=85),) \
+        in lister.run.call_args_list
+
+
+@patch('swh.lister.gitlab.tasks.GitLabLister')
+def test_relister_instance(lister, swh_app, celery_session_worker):
+    # setup the mocked GitlabLister
+    lister.return_value = lister
+    lister.run.return_value = None
+    lister.get_pages_information.return_value = (None, 85, None)
+    lister.db_partition_indices.return_value = [
+        (i, i+9) for i in range(0, 80, 10)] + [(80, 85)]
+
+    res = swh_app.send_task(
+        'swh.lister.gitlab.tasks.FullGitLabRelister',
+        kwargs=dict(api_baseurl='https://0xacab.org/api/v4'))
+    assert res
+
+    res.wait()
+    assert res.successful()
+
+    # retrieve the GroupResult for this task and wait for all the subtasks
+    # to complete
+    promise_id = res.result
+    assert promise_id
+    promise = GroupResult.restore(promise_id, app=swh_app)
+    for i in range(5):
+        if promise.ready():
+            break
+        sleep(1)
+
+    lister.assert_called_with(
+        api_baseurl='https://0xacab.org/api/v4',
+        instance=None, sort='asc', per_page=20)
 
     # one by the FullGitlabRelister task
     # + 9 for the RangeGitlabLister subtasks