diff --git a/includes/purl_path.inc b/includes/purl_path.inc
index bd15c7a..f232517 100644
--- a/includes/purl_path.inc
+++ b/includes/purl_path.inc
@@ -47,6 +47,16 @@ class purl_path implements purl_processor {
    * by processors.
    */
   public function adjust(&$value, $item, &$q) {
+    // We attempt to remove the prefix from the path as a way to detect it's
+    // presence. If the processor can remove itself than we're on a system path
+    // that contains our prefix. Then $alt will not be the same as the $path 
+    // and we won't do any rewriting.
+    if ($menu_item = menu_get_item($q)) {
+      $alt = $this->remove($q, $item);
+      if ($alt !== $q) {
+        return;
+      }
+    }
     $q = $this->remove($q, $item);
     $value = $this->remove($value, $item);
   }