diff --git a/tests/test_install.py b/tests/test_install.py
index 4da52996..c4dbb4ba 100644
--- a/tests/test_install.py
+++ b/tests/test_install.py
@@ -1045,6 +1045,9 @@ class DetectionFollowsTheRegistry(unittest.TestCase):
             env = {
                 "HOME": str(root / "home"), "APPDATA": str(root / "appdata"),
                 "ProgramFiles": str(root / "pf"), "ProgramFiles(x86)": str(root / "pf86"),
+                # Not the host's: a WSL session can hold them.
+                "USERPROFILE": "", "LOCALAPPDATA": "", "ProgramData": "",
+                "SCOOP": "", "SCOOP_GLOBAL": "",
             }
 
             def expand(text: str) -> str:
diff --git a/tests/test_install_selection.py b/tests/test_install_selection.py
index 97b969b3..07ac982f 100644
--- a/tests/test_install_selection.py
+++ b/tests/test_install_selection.py
@@ -362,7 +362,10 @@ class DecliningTheSizePointsAtTheChoice(unittest.TestCase):
     def _run(self, answers: list[str], *options: str) -> str:
         replies = iter(answers)
         out = io.StringIO()
-        with FakeRepository() as repo, \
+        # main() on a WSL host reads the Windows variables through cmd.exe
+        # and sets them in os.environ: restored here, they leaked into every
+        # later test (USERPROFILE added a Scoop folder to detection).
+        with FakeRepository() as repo, mock.patch.dict(os.environ), \
                 mock.patch.object(sys, "argv", ["install.py", "--platform", "retroarch",
                                                 "--dest", str(repo.dest), *options]), \
                 mock.patch.object(install, "MANIFEST_URL",