diff --git a/core/modules/user/src/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php b/core/modules/user/src/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php
index c00509f..5618605 100644
--- a/core/modules/user/src/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php
+++ b/core/modules/user/src/Plugin/LanguageNegotiation/LanguageNegotiationUserAdmin.php
@@ -127,10 +127,14 @@ protected function isAdminPath(Request $request) {
       $route_match = $this->stackedRouteMatch->getRouteMatchFromRequest($request);
       if ($route_match && !$route_object = $route_match->getRouteObject()) {
         try {
+          // Some inbound path processors make changes to the request. Make a
+          // copy as we're not actually routing the request so we do not want to
+          // make changes.
+          $cloned_request = clone $request;
           // Process the path as an inbound path. This will remove any language
           // prefixes and other path components that inbound processing would
           // clear out, so we can attempt to load the route clearly.
-          $path = $this->pathProcessorManager->processInbound(urldecode(rtrim($request->getPathInfo(), '/')), $request);
+          $path = $this->pathProcessorManager->processInbound(urldecode(rtrim($cloned_request->getPathInfo(), '/')), $cloned_request);
           $attributes = $this->router->match($path);
         }
         catch (ResourceNotFoundException $e) {