diff --git a/core/lib/Drupal/Core/PathProcessor/PathProcessorAccept.php b/core/lib/Drupal/Core/PathProcessor/PathProcessorAccept.php
index c5b1cec..9865612 100644
--- a/core/lib/Drupal/Core/PathProcessor/PathProcessorAccept.php
+++ b/core/lib/Drupal/Core/PathProcessor/PathProcessorAccept.php
@@ -28,9 +28,9 @@ public function processInbound($path, Request $request) {
     if (preg_match('/\.([a-z_]+)$/', $path, $match)) {
       if (isset($this->mapping[$match[1]])) {
         $request->setRequestFormat($this->mapping[$match[1]]);
+        // -1 for the dot.
+        $path = substr($path, 0, strlen($path) - strlen($match[1]) - 1);
       }
-      // -1 for the dot.
-      $path = substr($path, 0, strlen($path) - strlen($match[1]) - 1);
     }
     return $path;
   }