diff --git a/.eslintrc.json b/.eslintrc.json
index a957e1335..b5ae04c04 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -117,7 +117,7 @@
     "idbDel": "readonly",
     "idbAdd": "readonly",
     "idbCount": "readonly",
-    "idbClean": "readonly",
+    "idbFolderCleanup": "readonly",
     "initChangelog": "readonly",
     "sendNotification": "readonly",
     "monitorConnection": "readonly"
diff --git a/javascript/gallery.js b/javascript/gallery.js
index 028f622c1..ca1e524d5 100644
--- a/javascript/gallery.js
+++ b/javascript/gallery.js
@@ -635,7 +635,7 @@ async function thumbCacheCleanup(folder, imgCount) {
 
   idbIsCleaning = true;
   const [updateCleaningMsg, removeOverlayFunc] = showCleaningMsg();
-  idbClean(staticGalleryHashes, folder, updateCleaningMsg)
+  idbFolderCleanup(staticGalleryHashes, folder, updateCleaningMsg)
     .then((delcount) => {
       const t1 = performance.now();
       log(`Thumbnail DB cleanup: folder=${folder} kept=${staticGalleryHashes.size} deleted=${delcount} time=${Math.floor(t1 - t0)}ms`);
diff --git a/javascript/indexdb.js b/javascript/indexdb.js
index 490eb46f6..0adb76b57 100644
--- a/javascript/indexdb.js
+++ b/javascript/indexdb.js
@@ -123,16 +123,15 @@ async function idbCount(folder = null) {
  * @param {string} folder - Folder name/path
  * @param {updateMsgCallback} msgCallback - Callback for updating progress display
  */
-async function idbClean(keepSet, folder, msgCallback) {
+async function idbFolderCleanup(keepSet, folder, msgCallback) {
   if (!db) return null;
   if (!(keepSet instanceof Set)) {
-    throw new TypeError('IndexedDB cleaning function must be given a Set() of hashes to keep');
+    throw new TypeError('IndexedDB cleaning function must be given a Set() of the current gallery hashes');
   }
-  if (!folder) {
+  if (!folder || typeof folder !== 'string') {
     throw new Error('IndexedDB cleaning function must be told the current active folder');
   }
-  const folderCached = new Set(await idbGetAllKeys('folder', folder));
-  const removals = folderCached.difference(keepSet);
+  const removals = (new Set(await idbGetAllKeys('folder', folder))).difference(keepSet);
   const totalRemovals = removals.size;
   let counter = 0;
   return new Promise((resolve, reject) => {