diff --git a/packages/next/src/build/index.ts b/packages/next/src/build/index.ts
index 0b7378cc0171e7..96f02bff0a4d3d 100644
--- a/packages/next/src/build/index.ts
+++ b/packages/next/src/build/index.ts
@@ -287,6 +287,12 @@ export interface DynamicSsgRoute {
    * The status code that should be used when serving the fallback.
    */
   fallbackStatus?: number
+
+  /**
+   * The root params that are unknown for this fallback route.
+   */
+  fallbackRootParams: readonly string[] | undefined
+
   prefetchDataRoute: string | null | undefined
   prefetchDataRouteRegex: string | null | undefined
   routeRegex: string
@@ -3154,6 +3160,7 @@ export default async function build(
                   fallbackRevalidate,
                   fallbackStatus: meta.status,
                   fallbackHeaders: meta.headers,
+                  fallbackRootParams: route.fallbackRootParams,
                   dataRouteRegex: !dataRoute
                     ? null
                     : normalizeRouteRegex(
@@ -3581,6 +3588,7 @@ export default async function build(
                 ? `${normalizedRoute}.html`
                 : false,
             fallbackRevalidate: undefined,
+            fallbackRootParams: undefined,
             dataRouteRegex: normalizeRouteRegex(
               getNamedRouteRegex(
                 dataRoute.replace(/\.json$/, ''),