vercel/next.js · error

Duplicate page detected. ${cyan(existingPagePath)} and ${cya

Error message

Duplicate page detected. ${cyan(existingPagePath)} and ${cyan(duplicatePagePath)} both resolve to ${cyan(pageName)}.

What it means

Warning from the dev bundler's route watcher in setup-dev-bundler: while indexing page files it found two distinct files (existingPagePath and duplicatePagePath, highlighted in cyan) that both resolve to the same route name pageName — typically the same path existing under both app/ and pages/ directories, or conflicting extensions. Both would serve the same route, so the watcher flags the collision.

Source

Thrown at packages/next/src/server/lib/router-utils/setup-dev-bundler.ts:787

          if (routedPages.includes(pageName)) continue
        } else {
          // Pages router
          const existingPageFilePath = pagesPageFilePaths.get(pageName)
          if (pagesDir && existingPageFilePath) {
            duplicatePagePaths.add(pageName)

            if (!previousDuplicatePagePaths.has(pageName)) {
              const existingPagePath = normalizePathSep(
                path.join(
                  'pages',
                  path.relative(pagesDir, existingPageFilePath)
                )
              )
              const duplicatePagePath = normalizePathSep(
                path.join('pages', path.relative(pagesDir, fileName))
              )

              Log.warn(
                `Duplicate page detected. ${cyan(
                  existingPagePath
                )} and ${cyan(duplicatePagePath)} both resolve to ${cyan(
                  pageName
                )}.`
              )
            }
          }

          if (useFileSystemPublicRoutes) {
            pageFiles.add(pageName)
            opts.fsChecker.nextDataRoutes.add(pageName)
          }

          const route = normalizePathSep(pageName)
          const routeEntry = { route, filePath: fileName }
          if (isAPIRoute(pageName)) {
            pageApiRoutes.push(routeEntry)

View on GitHub (pinned to 258b1c1bc0)

Solutions

  1. Rename or remove one of the duplicate pages so only one file resolves to the route.
Defensive patterns

Strategy: validation

When it happens

Trigger: Thrown at packages/next/src/server/lib/router-utils/setup-dev-bundler.ts:769 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of vercel/next.js@258b1c1bc0 (2026-08-19). Data as JSON: /api/errors/333f50ddaa7c1e50. Report an issue: GitHub.