diff -u b/amp.module b/amp.module
--- b/amp.module
+++ b/amp.module
@@ -346,9 +346,9 @@
       $non_amp_path = substr($path, strlen('amp/'), strlen($path));
       break;
   }
-  if ($system_path = drupal_lookup_path('source', $non_amp_path, $path_language)) {
-    $path = $system_path;
-  }
+  $system_path = drupal_lookup_path('source', $non_amp_path, $path_language);
+  $path = $system_path ?: $non_amp_path;
+
   menu_set_active_item($path);
 }
 
@@ -377,7 +377,10 @@
         break;
     }
 
-    if ($is_amp_path) {
+    // Check that the path format is a valid amp format,
+    // and that original path isn't an already registered route.
+    // @TODO These amp paths should really be registered as system routes.
+    if ($is_amp_path && !(drupal_valid_path($current_path) && $current_path !== $non_amp_path)) {
       // Ensure that there is a node loaded from the current request, and that
       // it is a node type which has the AMP view mode enabled.
       $non_amp_path = drupal_get_normal_path($non_amp_path);