diff --git a/packages/core/src/lib/callback-handler.ts b/packages/core/src/lib/callback-handler.ts
index bae3ade9..4250a6fd 100644
--- a/packages/core/src/lib/callback-handler.ts
+++ b/packages/core/src/lib/callback-handler.ts
@@ -158,7 +158,7 @@ export async function handleLogin(
     const { provider: p } = options as InternalOptions<"oauth" | "oidc">
     const { type, provider, providerAccountId, userId, ...tokenSet } = account
     const defaults = { providerAccountId, provider, type, userId }
-    account = Object.assign(p.account(tokenSet), defaults)
+    account = Object.assign(p.account(tokenSet) ?? {}, defaults)
 
     if (user) {
       // If the user is already signed in and the OAuth account isn't already associated
diff --git a/packages/core/src/providers/oauth.ts b/packages/core/src/providers/oauth.ts
index 43cf759a..e7657885 100644
--- a/packages/core/src/providers/oauth.ts
+++ b/packages/core/src/providers/oauth.ts
@@ -95,7 +95,7 @@ export type ProfileCallback<Profile> = (
   tokens: TokenSet
 ) => Awaitable<User>
 
-export type AccountCallback = (tokens: TokenSet) => TokenSet
+export type AccountCallback = (tokens: TokenSet) => TokenSet | undefined | void
 
 export interface OAuthProviderButtonStyles {
   logo: string