diff --git a/category_handler.php b/category_handler.php
index 4d030ad29..f5cea9fa6 100644
--- a/category_handler.php
+++ b/category_handler.php
@@ -71,7 +71,7 @@ function updateIconBlob($catId, $iconData, $iconMimeType) {
   if (!dbi_execute(
     'DELETE FROM webcal_entry_categories
     WHERE cat_id = ? AND ( cat_owner = ?'
-      . ($is_admin ? ' OR cat_owner = '' )' : ' )'),
+      . ($is_admin ? ' OR cat_owner = "" )' : ' )'),
     [$id, $login]
   )) {
     $error = db_error();