diff --git a/js/pacosako_ui.js b/js/pacosako_ui.js
index 6bfb208..2ad798d 100644
--- a/js/pacosako_ui.js
+++ b/js/pacosako_ui.js
@@ -436,6 +436,112 @@ $(function (){
       putMeta({ board: moves });
    }
 
+   let noticeBox = null;
+
+   function openNoticeBox(content) {
+      if (noticeBox) {
+         noticeBox.setContent(content);
+         noticeBox.open();
+      } else {
+         noticeBox = new jBox('Notice', {
+            autoClose: false,
+            closeOnEsc: false,
+            closeOnClick: false,
+            content: content,
+            delayClose: 2000,
+            delayOpen: 100,
+            onClose() {
+               if (noticeBox === this) {
+                  noticeBox = null;
+               }
+            },
+            onCloseComplete() {
+               this.destroy();
+            },
+         });
+      }
+   }
+
+   const updateQueue = {
+      head: 0,  /* next item to be sent */
+      tail: 0,  /* ID to assign to the next update added to the queue */
+      lastGameId: null,
+      lastModified: null,
+      newModified: 0,
+      sending: false,
+
+      add(gameId, data, modified) {
+         const wasEmpty = this.head === this.tail;
+         data = Object.assign({}, data, { modified });
+
+         this[this.tail] = { gameId, data, modified };
+         this.tail += 1;
+
+         if (!this.sending) {
+            openNoticeBox('Saving...');
+            this.sending = true;
+            this.sendNext();
+         }
+      },
+
+      sendNext() {
+         const queue = this;
+
+         if (queue.head === queue.tail) {
+            return;
+         }
+
+         const update = queue[queue.head];
+         delete queue[queue.head];
+         queue.head += 1;
+
+         if (update.gameId === queue.lastGameId && update.modified === queue.lastModified) {
+            update.data.modified = queue.newModified;
+         }
+
+         IO.sendUpdate(update.gameId, update.data).then((response) => {
+            queue.lastGameId = update.gameId;
+            if (response && response.data && 'modified' in response.data) {
+               /*
+                * If we queued two or more updates with the same .modified (thus
+                * based on the same server data), send the next update with the
+                * new .modified assigned by the server as a result of this update.
+                */
+               queue.lastModified = update.modified; /* original, not adjusted */
+               queue.newModified = response.data.modified;
+            } else {
+               queue.lastModified = null;
+               queue.newModified = 0;
+            }
+
+            if (queue.head === queue.tail) {
+               queue.sending = false;
+               /* close the Saving... notice*/
+               noticeBox.close({ ignoreDelay: true });
+            } else {
+               queue.sendNext();
+            }
+         }).catch((err) => {
+            openNoticeBox('Failed to send update to server.');
+            noticeBox.close();
+            debug('update error', err);
+
+            /* additional updates are unlikely to succeed, so empty the queue */
+            while (queue.head < queue.tail) {
+               delete queue[queue.head];
+               queue.head += 1;
+            }
+
+            queue.sending = false;
+
+            /* force a reset back to the latest server data */
+            if (update.gameId === $('#cb_board').data('gameId')) {
+               switchGameId(update.gameId, true);
+            }
+         });
+      },
+   };
+
    function putMeta(extra) {
       const gameId = $('#cb_board').data('gameId');
       const lightName = $('#cb_light_name').val();
@@ -462,30 +568,7 @@ $(function (){
          Object.assign(meta, extra);
       }
 
-      const noticeBox = new jBox('Notice', {
-         content: 'Saving...',
-         autoClose: false,
-         delayOpen: 200,
-         delayClose: 2000,
-         onCloseComplete() { this.destroy(); },
-      });
-
-      const modified = meta.modified = $('#cb_board').data('modified');
-      IO.sendUpdate(gameId, meta).then((response) => {
-         noticeBox.close({ ignoreDelay: true });
-         if (response && response.data && Number.isInteger(response.data.modified)) {
-            if (response.data.modified > modified) {
-               $('#cb_board').data('modified', response.data.modified);
-            }
-         }
-      }).catch((err) => {
-         noticeBox.setContent('Failed to send update to server.');
-         noticeBox.close();
-         debug('update error', err);
-
-         /* force a reset back to the latest server data */
-         switchGameId(gameId, true);
-      });
+      updateQueue.add(gameId, meta, $('#cb_board').data('modified'));
    }
 
    function switchGameId(newId, force) {