diff --git a/src/calibre/srv/books.py b/src/calibre/srv/books.py
index 29b2d18ea0..95544115f2 100644
--- a/src/calibre/srv/books.py
+++ b/src/calibre/srv/books.py
@@ -8,7 +8,7 @@ import os
 import tempfile
 import time
 from functools import partial
-from hashlib import sha1
+from hashlib import sha256
 from threading import Lock, RLock
 
 from calibre.constants import cache_dir, iswindows
@@ -58,7 +58,7 @@ def books_cache_dir():
 
 def book_hash(library_uuid, book_id, fmt, size, mtime):
     raw = json_dumps((library_uuid, book_id, fmt.upper(), size, mtime, RENDER_VERSION))
-    return as_unicode(sha1(raw).hexdigest())
+    return as_unicode(sha256(raw).hexdigest())
 
 
 staging_cleaned = False
diff --git a/src/calibre/srv/code.py b/src/calibre/srv/code.py
index 4f49976cae..29ba31cdaf 100644
--- a/src/calibre/srv/code.py
+++ b/src/calibre/srv/code.py
@@ -455,7 +455,7 @@ def tag_browser(ctx, rd):
     opts = categories_settings(rd.query, db, gst_container=tuple)
     vl = rd.query.get('vl') or ''
     etag = json_dumps([db.last_modified().isoformat(), rd.username, library_id, vl, list(opts)])
-    etag = hashlib.sha1(etag).hexdigest()
+    etag = hashlib.sha256(etag).hexdigest()
 
     def generate():
         return json(ctx, rd, tag_browser, categories_as_json(ctx, rd, db, opts, vl))