diff --git a/README.md b/README.md
index 47a2da7..3147352 100644
--- a/README.md
+++ b/README.md
@@ -34,15 +34,7 @@ const providers: OAuthLoginProviders = {
   [CODEX_PROVIDER]: {
     oauthConfig: codexOAuthConfig,
     exchange: (code, verifier, now) => exchangeCodexCode(code, verifier, now),
-    // `refresh` only ever receives the stored refresh secret, so the prior
-    // tokens passed here supply just that; refreshCodexTokens carries the
-    // account id forward from a caller-supplied `previous` only when the
-    // refresh response itself omits `id_token`, which it usually does.
-    refresh: (refreshSecret, now) =>
-      refreshCodexTokens(refreshSecret, now, {
-        access: "",
-        refresh: refreshSecret,
-      }),
+    refresh: (refreshSecret, now) => refreshCodexTokens(refreshSecret, now),
     // The Codex backend rejects inference without this header value.
     metadata: (tokens) =>
       "accountId" in tokens && typeof tokens.accountId === "string"
diff --git a/src/oauth.test.ts b/src/oauth.test.ts
index c784974..6f8b30a 100644
--- a/src/oauth.test.ts
+++ b/src/oauth.test.ts
@@ -55,4 +55,15 @@ describe("Codex oauth — refresh account id continuity", () => {
     );
     expect(refreshed.accountId).toBe("acct-1");
   });
+
+  test("keeps the refresh token and leaves the account id unset without previous tokens", async () => {
+    const refreshed = await refreshCodexTokens(
+      "refresh-1",
+      0,
+      undefined,
+      fetchResolving({ access_token: "new" }),
+    );
+    expect(refreshed.refresh).toBe("refresh-1");
+    expect(refreshed.accountId).toBeUndefined();
+  });
 });
diff --git a/src/oauth.ts b/src/oauth.ts
index 21a80ff..16a3e9f 100644
--- a/src/oauth.ts
+++ b/src/oauth.ts
@@ -104,13 +104,14 @@ export async function exchangeCodexCode(
  * Refreshes a Codex access token, carrying the prior refresh token forward
  * when the response omits it. A refresh response frequently omits
  * `id_token` entirely, which would otherwise drop `chatgpt-account-id` from
- * every request after the first refresh — the caller's `previous` tokens
- * supply the account id to carry forward in that case.
+ * every request after the first refresh. Pass the caller's `previous` tokens
+ * to carry their account id forward in that case; without them, the caller
+ * keeps the account id some other way (for example, in credential metadata).
  */
 export async function refreshCodexTokens(
   refreshToken: string,
   now: number,
-  previous: CodexTokens,
+  previous?: CodexTokens,
   fetchImpl: FetchLike = fetch,
 ): Promise<CodexTokens> {
   const refreshed = codexTokensFromResponse(
@@ -120,7 +121,7 @@ export async function refreshCodexTokens(
   );
   return {
     ...refreshed,
-    ...(refreshed.accountId === undefined && previous.accountId !== undefined
+    ...(refreshed.accountId === undefined && previous?.accountId !== undefined
       ? { accountId: previous.accountId }
       : {}),
   };