diff --git a/internal/router/ui.go b/internal/router/ui.go
index 14f71f5fc..0094b78b9 100644
--- a/internal/router/ui.go
+++ b/internal/router/ui.go
@@ -69,6 +69,19 @@ func (r *_resource) Open(name string) (fs.File, error) {
 	return r.fs.Open(name)
 }
 
+// isMissingStaticAsset reports whether the request targets a file under /static that does not exist.
+// gin falls through to NoRoute for such paths, and answering with index.html (200) makes the browser
+// parse HTML as JavaScript after an upgrade, when a stale tab requests chunks of the previous build.
+func isMissingStaticAsset(urlPath, baseURLPath string) bool {
+	if len(baseURLPath) > 0 {
+		if !strings.HasPrefix(urlPath, baseURLPath) {
+			return false
+		}
+		urlPath = strings.TrimPrefix(urlPath, baseURLPath)
+	}
+	return strings.HasPrefix(urlPath, "/static/")
+}
+
 // Register a new static resource which generated by ui directory
 func (a *UIRouter) Register(r *gin.Engine, baseURLPath string) {
 	staticPath := os.Getenv("ANSWER_STATIC_PATH")
@@ -85,6 +98,10 @@ func (a *UIRouter) Register(r *gin.Engine, baseURLPath string) {
 			r.LoadHTMLGlob(staticPath + "/*.html")
 			r.Static(baseURLPath+"/static", staticPath+"/static")
 			r.NoRoute(func(c *gin.Context) {
+				if isMissingStaticAsset(c.Request.URL.Path, baseURLPath) {
+					c.AbortWithStatus(http.StatusNotFound)
+					return
+				}
 				c.HTML(http.StatusOK, "index.html", gin.H{})
 			})
 
@@ -100,6 +117,10 @@ func (a *UIRouter) Register(r *gin.Engine, baseURLPath string) {
 
 	// specify the not router for default routes and redirect
 	r.NoRoute(func(c *gin.Context) {
+		if isMissingStaticAsset(c.Request.URL.Path, baseURLPath) {
+			c.AbortWithStatus(http.StatusNotFound)
+			return
+		}
 		urlPath := c.Request.URL.Path
 		if len(baseURLPath) > 0 {
 			urlPath = strings.TrimPrefix(urlPath, baseURLPath)
diff --git a/internal/router/ui_test.go b/internal/router/ui_test.go
index 645529338..e380699f4 100644
--- a/internal/router/ui_test.go
+++ b/internal/router/ui_test.go
@@ -19,41 +19,25 @@
 
 package router
 
-import (
-	"errors"
-	"net/http"
-	"net/http/httptest"
-	"testing"
-
-	"github.com/apache/answer/internal/service/mock"
-	"github.com/gin-gonic/gin"
-	"github.com/stretchr/testify/assert"
-	"go.uber.org/mock/gomock"
-)
-
-func TestUIRouter_FaviconWithNilBranding(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-
-	mockSiteInfoService := mock.NewMockSiteInfoCommonService(ctrl)
-
-	// Simulate a database error
-	mockSiteInfoService.EXPECT().
-		GetSiteBranding(gomock.Any()).
-		Return(nil, errors.New("database connection failed"))
-
-	router := &UIRouter{
-		siteInfoService: mockSiteInfoService,
+import "testing"
+
+func TestIsMissingStaticAsset(t *testing.T) {
+	cases := []struct {
+		name, urlPath, base string
+		want                bool
+	}{
+		{"chunk of a previous build", "/static/js/6487.02e56745.chunk.js", "", true},
+		{"with base url", "/answer/static/css/main.css", "/answer", true},
+		{"spa route", "/users/alice", "", false},
+		{"spa route with base url", "/answer/questions", "/answer", false},
+		{"static under a different base", "/static/js/main.js", "/answer", false},
+		{"root", "/", "", false},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			if got := isMissingStaticAsset(c.urlPath, c.base); got != c.want {
+				t.Fatalf("isMissingStaticAsset(%q, %q) = %v, want %v", c.urlPath, c.base, got, c.want)
+			}
+		})
 	}
-
-	gin.SetMode(gin.TestMode)
-	r := gin.New()
-	router.Register(r, "")
-
-	req := httptest.NewRequest(http.MethodGet, "/favicon.ico", nil)
-	w := httptest.NewRecorder()
-
-	r.ServeHTTP(w, req)
-
-	assert.Equal(t, http.StatusOK, w.Code)
 }
diff --git a/ui/src/router/index.tsx b/ui/src/router/index.tsx
index ea2fdf3c2..2a6db31a4 100644
--- a/ui/src/router/index.tsx
+++ b/ui/src/router/index.tsx
@@ -27,6 +27,8 @@ import baseRoutes, { RouteNode } from './routes';
 import RouteGuard from './RouteGuard';
 import RouteErrorBoundary from './RouteErrorBoundary';
 
+const STALE_CHUNK_KEY = 'answer_stale_chunk_reload';
+
 const routeWrapper = (routeNodes: RouteNode[], root: RouteNode[]) => {
   routeNodes.forEach((rn) => {
     if (rn.page === 'pages/Layout') {
@@ -48,7 +50,25 @@ const routeWrapper = (routeNodes: RouteNode[], root: RouteNode[]) => {
 
       if (typeof rn.page === 'string') {
         const pagePath = rn.page.replace('pages/', '');
-        Ctrl = lazy(() => import(`@/pages/${pagePath}`));
+        Ctrl = lazy(() =>
+          import(`@/pages/${pagePath}`).then(
+            (m) => {
+              sessionStorage.removeItem(STALE_CHUNK_KEY);
+              return m;
+            },
+            (err) => {
+              // A tab opened before an upgrade still runs the old bundle; the hashed chunk
+              // names it asks for no longer exist on the server, so reload once to pick up
+              // the new index.html instead of rendering the 50X error page.
+              if (!sessionStorage.getItem(STALE_CHUNK_KEY)) {
+                sessionStorage.setItem(STALE_CHUNK_KEY, '1');
+                window.location.reload();
+                return new Promise<never>(() => {});
+              }
+              throw err;
+            },
+          ),
+        );
       } else {
         Ctrl = rn.page;
       }