diff --git a/packages/next/export/worker.ts b/packages/next/export/worker.ts
index 180def8d1cd2..dca36f816615 100644
--- a/packages/next/export/worker.ts
+++ b/packages/next/export/worker.ts
@@ -215,8 +215,8 @@ export default async function exportPage({
         subFolders ? `${_path}${sep}index.html` : `${_path}.html`
       let htmlFilename = getHtmlFilename(filePath)
 
-      const pageExt = extname(page)
-      const pathExt = extname(path)
+      const pageExt = isDynamic ? '' : extname(page)
+      const pathExt = isDynamic ? '' : extname(path)
       // Make sure page isn't a folder with a dot in the name e.g. `v1.2`
       if (pageExt !== pathExt && pathExt !== '') {
         const isBuiltinPaths = ['/500', '/404'].some(
diff --git a/packages/next/server/denormalize-page-path.ts b/packages/next/server/denormalize-page-path.ts
index 39ba36212f69..e3e2f1bcecd0 100644
--- a/packages/next/server/denormalize-page-path.ts
+++ b/packages/next/server/denormalize-page-path.ts
@@ -1,10 +1,12 @@
+import { isDynamicRoute } from '../shared/lib/router/utils'
+
 export function normalizePathSep(path: string): string {
   return path.replace(/\\/g, '/')
 }
 
 export function denormalizePagePath(page: string) {
   page = normalizePathSep(page)
-  if (page.startsWith('/index/')) {
+  if (page.startsWith('/index/') && !isDynamicRoute(page)) {
     page = page.slice(6)
   } else if (page === '/index') {
     page = '/'
diff --git a/packages/next/server/normalize-page-path.ts b/packages/next/server/normalize-page-path.ts
index 95e8d9a596c6..0c25c4ad1f3f 100644
--- a/packages/next/server/normalize-page-path.ts
+++ b/packages/next/server/normalize-page-path.ts
@@ -6,7 +6,7 @@ export function normalizePagePath(page: string): string {
   // If the page is `/` we need to append `/index`, otherwise the returned directory root will be bundles instead of pages
   if (page === '/') {
     page = '/index'
-  } else if (/^\/index(\/|$)/.test(page)) {
+  } else if (/^\/index(\/|$)$/.test(page)) {
     page = `/index${page}`
   }
   // Resolve on anything that doesn't start with `/`
diff --git a/packages/next/shared/lib/router/utils/get-route-from-asset-path.ts b/packages/next/shared/lib/router/utils/get-route-from-asset-path.ts
index 495865e56876..b738e75c74f0 100644
--- a/packages/next/shared/lib/router/utils/get-route-from-asset-path.ts
+++ b/packages/next/shared/lib/router/utils/get-route-from-asset-path.ts
@@ -1,4 +1,7 @@
 // Translate a pages asset path (relative from a common prefix) back into its logical route
+
+import { isDynamicRoute } from './is-dynamic'
+
 // "asset path" being its javascript file, data file, prerendered html,...
 export default function getRouteFromAssetPath(
   assetPath: string,
@@ -7,7 +10,7 @@ export default function getRouteFromAssetPath(
   assetPath = assetPath.replace(/\\/g, '/')
   assetPath =
     ext && assetPath.endsWith(ext) ? assetPath.slice(0, -ext.length) : assetPath
-  if (assetPath.startsWith('/index/')) {
+  if (assetPath.startsWith('/index/') && !isDynamicRoute(assetPath)) {
     assetPath = assetPath.slice(6)
   } else if (assetPath === '/index') {
     assetPath = '/'
diff --git a/test/integration/dynamic-routing/pages/index/[...slug].js b/test/integration/dynamic-routing/pages/index/[...slug].js
new file mode 100644
index 000000000000..0688517139fd
--- /dev/null
+++ b/test/integration/dynamic-routing/pages/index/[...slug].js
@@ -0,0 +1,3 @@
+export default function page() {
+  return 'index/[...slug]'
+}