diff --git a/src/auth/login.ts b/src/auth/login.ts
index 4123b1b..fac00eb 100644
--- a/src/auth/login.ts
+++ b/src/auth/login.ts
@@ -76,8 +76,12 @@ const srpHandshake = async (
     // twoFactorSessionIDV2 is set (instead of twoFactorSessionID) when the
     // account has BOTH passkeys and TOTP. Prefer TOTP: a CLI cannot perform
     // a WebAuthn ceremony, and the user has a TOTP secret enrolled.
+    //
+    // The server marshals these fields without `omitempty`, so unset fields
+    // arrive as "" rather than being absent. Use || (not ??) so empty
+    // strings are treated as not-set.
     const totpSessionID =
-        verifyResponse.twoFactorSessionID ??
+        verifyResponse.twoFactorSessionID ||
         verifyResponse.twoFactorSessionIDV2;
     if (totpSessionID) {
         return { kind: "totp", sessionID: totpSessionID };