diff --git a/src/pas/plugins/oidc/plugins.py b/src/pas/plugins/oidc/plugins.py
index 90b17b9..05ebe86 100644
--- a/src/pas/plugins/oidc/plugins.py
+++ b/src/pas/plugins/oidc/plugins.py
@@ -369,7 +369,8 @@ def get_oauth2_client(self):
                 # - modify the keybundle objects after provider_config but before they are used.
                 #   - client.keyjar.issuer_keys[issuer].source = ...
                 for key in client.keyjar.issuer_keys[self.getProperty("issuer")]:
-                    key.source = requests.PreparedRequest().prepare_request(key.source, dict(identityDomainName=domain)).url
+                    req = requests.PreparedRequest()
+                    key.source = req.prepare_url(key.source, dict(identityDomainName=domain)).url
             info = {
                 "client_id": self.getProperty("client_id"),
                 "client_secret": self.getProperty("client_secret"),