diff --git a/sso-mfa/k8s/keycape/test_adapter_source_closure.py b/sso-mfa/k8s/keycape/test_adapter_source_closure.py
index d44ac8b..6b6da3d 100644
--- a/sso-mfa/k8s/keycape/test_adapter_source_closure.py
+++ b/sso-mfa/k8s/keycape/test_adapter_source_closure.py
@@ -48,9 +48,19 @@ print(json.dumps({'loaded': sorted(set(local)), 'pinned': sorted(pinned)}))
 KNOWN_FAILING = set()
 
 
+def _probe_env():
+    # The probe runs with cwd=ROOT, so a relative PYTHONPATH entry would stop
+    # pointing where the caller meant it to; resolve entries against our cwd.
+    env = dict(os.environ)
+    if env.get('PYTHONPATH'):
+        env['PYTHONPATH'] = os.pathsep.join(
+            str(Path(p).resolve()) for p in env['PYTHONPATH'].split(os.pathsep) if p)
+    return env
+
+
 def probe(adapter):
     out = subprocess.run([sys.executable, '-c', PROBE, str(ROOT), str(REPO), adapter],
-                         capture_output=True, text=True, env=dict(os.environ), cwd=ROOT)
+                         capture_output=True, text=True, env=_probe_env(), cwd=ROOT)
     if out.returncode:
         raise AssertionError(f'{adapter} probe failed: {out.stderr[-2000:]}')
     return json.loads(out.stdout.strip().splitlines()[-1])