diff --git a/docs/example.nginx.conf b/docs/example.nginx.conf
index 5c4ff2fbe..9d856a5a9 100644
--- a/docs/example.nginx.conf
+++ b/docs/example.nginx.conf
@@ -46,6 +46,8 @@ server {
 
     set $unsafe 0;
     if ($uri = "/pad/inner.html") { set $unsafe 1; }
+    if ($uri = "/sheet/inner.html") { set $unsafe 1; }
+    if ($uri = "/common/onlyoffice/web-apps/apps/spreadsheeteditor/main/index.html") { set $unsafe 1; }
     if ($host != sandbox.cryptpad.info) { set $unsafe 0; }
     if ($unsafe) {
         set $scriptSrc "'self' 'unsafe-eval' 'unsafe-inline' new2.cryptpad.fr cryptpad.fr";
@@ -95,7 +97,7 @@ server {
         try_files $uri =404;
     }
 
-    location ~ ^/(register|login|settings|user|pad|drive|poll|slide|code|whiteboard|file|media|profile|contacts|todo|filepicker|debug|kanban)$ {
+    location ~ ^/(register|login|settings|user|pad|drive|poll|slide|code|whiteboard|file|media|profile|contacts|todo|filepicker|debug|kanban|sheet)$ {
         rewrite ^(.*)$ $1/ redirect;
     }
 
diff --git a/www/common/sframe-common.js b/www/common/sframe-common.js
index 1236d4fcd..d6cbfc350 100644
--- a/www/common/sframe-common.js
+++ b/www/common/sframe-common.js
@@ -201,7 +201,7 @@ define([
         if (typeof(channel) !== 'string' || channel.length !== Hash.ephemeralChannelLength) {
             channel = Hash.createChannelId(true); // true indicates that it's an ephemeral channel
         }
-        if (!md.cursor) {
+        if (md.cursor !== channel) {
             md.cursor = channel;
             ctx.metadataMgr.updateMetadata(md);
             setTimeout(saveChanges);
diff --git a/www/filepicker/main.js b/www/filepicker/main.js
index 596cc0a45..5792001e5 100644
--- a/www/filepicker/main.js
+++ b/www/filepicker/main.js
@@ -41,10 +41,34 @@ define([
             var Utils = config.modules.Utils;
 
             nThen(function (waitFor) {
-                config.modules.SFrameChannel.create($('#sbox-filePicker-iframe')[0].contentWindow,
-                    waitFor(function (sfc) {
+                // The inner iframe tries to get some data from us every ms (cache, store...).
+                // It will send a "READY" message and wait for our answer with the correct txid.
+                // First, we have to answer to this message, otherwise we're going to block
+                // sframe-boot.js. Then we can start the channel.
+                var msgEv = Utils.Util.mkEvent();
+                var iframe = $('#sbox-filePicker-iframe')[0].contentWindow;
+                var postMsg = function (data) {
+                    iframe.postMessage(data, '*');
+                };
+                var whenReady = waitFor(function (msg) {
+                    if (msg.source !== iframe) { return; }
+                    var data = JSON.parse(msg.data);
+                    if (!data.txid) { return; }
+                    // Remove the listener once we've received the READY message
+                    window.removeEventListener('message', whenReady);
+                    // Answer with the requested data
+                    postMsg(JSON.stringify({ txid: data.txid, language: Cryptpad.getLanguage() }));
+
+                    // Then start the channel
+                    window.addEventListener('message', function (msg) {
+                        if (msg.source !== iframe) { return; }
+                        msgEv.fire(msg);
+                    });
+                    config.modules.SFrameChannel.create(msgEv, postMsg, waitFor(function (sfc) {
                         sframeChan = sfc;
                     }));
+                });
+                window.addEventListener('message', whenReady);
             }).nThen(function () {
                 var updateMeta = function () {
                     //console.log('EV_METADATA_UPDATE');