diff --git a/src/gam/gapi/errors.py b/src/gam/gapi/errors.py
index 3a15bb67..05ce82af 100644
--- a/src/gam/gapi/errors.py
+++ b/src/gam/gapi/errors.py
@@ -225,6 +225,7 @@ OAUTH2_TOKEN_ERRORS = [
   'invalid_grant: Not a valid email',
   'invalid_grant: Invalid JWT: No valid verifier found for issuer',
   'invalid_request: Invalid impersonation prn email address',
+  'invalid_request: Invalid impersonation "sub" field',
   'unauthorized_client: Client is unauthorized to retrieve access tokens '
   'using this method',
   'unauthorized_client: Client is unauthorized to retrieve access tokens '