diff --git a/oidc-exchange.py b/oidc-exchange.py
index 7dea3b0..cfc31d9 100644
--- a/oidc-exchange.py
+++ b/oidc-exchange.py
@@ -247,7 +247,7 @@ except requests.JSONDecodeError:
 # occurred during minting.
 if not mint_token_resp.ok:
     reasons = '\n'.join(
-        f'* `{error['code']}`: {error['description']}'
+        f'* `{error["code"]}`: {error["description"]}'
         for error in mint_token_payload['errors']
     )