diff --git a/lib/filestorage/zip_archive.php b/lib/filestorage/zip_archive.php
index 70b9d336f5d..b7d0fd68dde 100644
--- a/lib/filestorage/zip_archive.php
+++ b/lib/filestorage/zip_archive.php
@@ -207,6 +207,12 @@ class zip_archive extends file_archive {
             $this->mode = null;
             $this->namelookup = null;
             $this->modified = false;
+            // If the existing archive is already empty, we didn't change it.  Don't bother completing a save.
+            // This is important when we are inspecting archives that we might not have write permission to.
+            if (@filesize($this->archivepathname) == 22 &&
+                    @file_get_contents($this->archivepathname) === base64_decode(self::$emptyzipcontent)) {
+                return true;
+            }
             @unlink($this->archivepathname);
             $data = base64_decode(self::$emptyzipcontent);
             if (!file_put_contents($this->archivepathname, $data)) {