Index: src/applications/project/editor/PhabricatorProjectEditor.php
===================================================================
--- src/applications/project/editor/PhabricatorProjectEditor.php
+++ src/applications/project/editor/PhabricatorProjectEditor.php
@@ -250,8 +250,8 @@
         $old_slug = $project->getFullPhrictionSlug();
         $project->setName($xaction->getNewValue());
         $project->setPhrictionSlug($xaction->getNewValue());
-
-        if ($xaction->getOldValue()) {
+        $changed_slug = $old_slug != $project->getFullPhrictionSlug();
+        if ($xaction->getOldValue() && $changed_slug) {
           $old_document = id(new PhrictionDocument())
             ->loadOneWhere(
               'slug = %s',