diff --git a/swh/lister/opam/lister.py b/swh/lister/opam/lister.py
index 098e4be..1fbc7db 100644
--- a/swh/lister/opam/lister.py
+++ b/swh/lister/opam/lister.py
@@ -1,95 +1,107 @@
 # Copyright (C) 2021  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import io
 import logging
 import os
 from subprocess import PIPE, Popen, call
 import tempfile
 from typing import Iterator
 
 from swh.lister.pattern import StatelessLister
 from swh.scheduler.interface import SchedulerInterface
 from swh.scheduler.model import ListedOrigin
 
 from ..pattern import CredentialsType
 
 logger = logging.getLogger(__name__)
 
 PageType = str
 
 
 class OpamLister(StatelessLister[PageType]):
     """
     List all repositories hosted on an opam repository.
 
     On initialisation, we create an opam root, with no ocaml compiler (no switch)
     as we won't need it and it's costly. In this opam root, we add a single opam
     repository (url) and give it a name (instance). Then, to get pages, we just ask
     opam to list all the packages for our opam repository in our opam root.
 
     Args:
         url: base URL of an opam repository
             (for instance https://opam.ocaml.org)
         instance: string identifier for the listed repository
 
     """
 
     # Part of the lister API, that identifies this lister
     LISTER_NAME = "opam"
 
     def __init__(
         self,
         scheduler: SchedulerInterface,
         url: str,
         instance: str,
         credentials: CredentialsType = None,
     ):
         super().__init__(
             scheduler=scheduler, credentials=credentials, url=url, instance=instance,
         )
         self.env = os.environ.copy()
-        self.env["OPAMROOT"] = tempfile.mkdtemp(prefix="swh_opam_lister")
+        self.opamroot = tempfile.mkdtemp(prefix="swh_opam_lister")
         call(
-            ["opam", "init", "--reinit", "--bare", "--no-setup", instance, url],
+            [
+                "opam",
+                "init",
+                "--reinit",
+                "--bare",
+                "--no-setup",
+                "--root",
+                self.opamroot,
+                instance,
+                url,
+            ],
             env=self.env,
         )
 
     def get_pages(self) -> Iterator[PageType]:
         proc = Popen(
             [
                 "opam",
                 "list",
                 "--all",
                 "--no-switch",
                 "--repos",
                 self.instance,
+                "--root",
+                self.opamroot,
                 "--normalise",
                 "--short",
             ],
             env=self.env,
             stdout=PIPE,
         )
         if proc.stdout is not None:
             for line in io.TextIOWrapper(proc.stdout):
                 yield line.rstrip("\n")
 
     def get_origins_from_page(self, page: PageType) -> Iterator[ListedOrigin]:
         """Convert a page of OpamLister repositories into a list of ListedOrigins"""
         assert self.lister_obj.id is not None
         # a page is just a package name
         url = f"opam+{self.url}/packages/{page}/"
         yield ListedOrigin(
             lister_id=self.lister_obj.id,
             visit_type="opam",
             url=url,
             last_update=None,
             extra_loader_arguments={
-                "opam_root": self.env["OPAMROOT"],
+                "opam_root": self.opamroot,
                 "opam_instance": self.instance,
                 "opam_url": self.url,
                 "opam_package": page,
             },
         )