diff --git a/copyparty/httpcli.py b/copyparty/httpcli.py
index bd9bb6c6..3390907d 100644
--- a/copyparty/httpcli.py
+++ b/copyparty/httpcli.py
@@ -2634,7 +2634,7 @@ class HttpCli(object):
         #
         # if request is for foo.js, check if we have foo.js.{gz,br}
 
-        file_ts = 0
+        file_ts = 0.0
         editions: dict[str, tuple[str, int]] = {}
         for ext in ["", ".gz", ".br"]:
             try:
@@ -2652,7 +2652,7 @@ class HttpCli(object):
                 else:
                     sz = st.st_size
 
-                file_ts = max(file_ts, int(st.st_mtime))
+                file_ts = max(file_ts, st.st_mtime)
                 editions[ext or "plain"] = (fs_path, sz)
             except:
                 pass
@@ -2665,11 +2665,14 @@ class HttpCli(object):
         #
         # if-modified
 
-        file_lastmod, do_send = self._chk_lastmod(file_ts)
+        file_lastmod, do_send = self._chk_lastmod(int(file_ts))
         self.out_headers["Last-Modified"] = file_lastmod
         if not do_send:
             status = 304
 
+        if self.can_write:
+            self.out_headers["X-Lastmod3"] = str(int(file_ts * 1000))
+
         #
         # Accept-Encoding and UA decides which edition to send
 
diff --git a/copyparty/web/md2.js b/copyparty/web/md2.js
index c33b506c..77fbc300 100644
--- a/copyparty/web/md2.js
+++ b/copyparty/web/md2.js
@@ -278,6 +278,7 @@ function Modpoll() {
             return;
 
         var new_md = this.responseText,
+            new_mt = this.getResponseHeader('X-Lastmod3') || r.lastmod,
             server_ref = server_md.replace(/\r/g, ''),
             server_now = new_md.replace(/\r/g, '');
 
@@ -285,6 +286,7 @@ function Modpoll() {
         if (r.initial && server_ref != server_now)
             return modal.confirm('Your browser decided to show an outdated copy of the document!\n\nDo you want to load the latest version from the server instead?', function () {
                 dom_src.value = server_md = new_md;
+                last_modified = new_mt;
                 draw_md();
             }, null);