diff --git a/system/Router/DefinedRouteCollector.php b/system/Router/DefinedRouteCollector.php
index 8d4f1dc5b1b7..2452a141fa75 100644
--- a/system/Router/DefinedRouteCollector.php
+++ b/system/Router/DefinedRouteCollector.php
@@ -38,6 +38,10 @@ public function collect(): Generator
             $routes = $this->routeCollection->getRoutes($method);
 
             foreach ($routes as $route => $handler) {
+                // The route key should be a string, but it is stored as an array key,
+                // it might be an integer.
+                $route = (string) $route;
+
                 if (is_string($handler) || $handler instanceof Closure) {
                     if ($handler instanceof Closure) {
                         $view = $this->routeCollection->getRoutesOptions($route, $method)['view'] ?? false;