I'm using Next.js 15 with the App Router, and I have a dynamic route: app/blog/[slug]/page.tsx.

Everything works fine at runtime, but during build I get this type error from an auto-generated file:

.next/types/app/blog/[slug]/page.ts:34:29
Type error: Type '{ params: { slug: string; } }' does not satisfy the constraint 'PageProps'.
  Types of property 'params' are incompatible.
    Type '{ slug: string; }' is missing the following properties from type 'Promise<any>': then, catch, finally, [Symbol.toStringTag]

This is strange because in my actual page.tsx, params is used like this:

export default async function BlogPost({
  params,
}: {
  params: { slug: string };
}) {
  const article = blogArticles.find((article) => article.slug === params.slug);
  if (!article) {
    notFound();
  }

  return (
    <DefaultLayout>
      <ArticleLayout
        title={article.title}
        date={article.date}
        image={article.image}
        duration={article.duration}
      >
        <ArticleBody slug={params.slug} />
      </ArticleLayout>
    </DefaultLayout>
  );
}

export async function generateMetadata({
  params,
}: {
  params: { slug: string };
}): Promise<Metadata> {
  ...
}

So far everything is working — until the build fails due to .next/types/....