diff --git a/app/assets/javascripts/discourse/components/topic-progress.js.es6 b/app/assets/javascripts/discourse/components/topic-progress.js.es6
index c4a4a4e7fcf..5a769dd5274 100644
--- a/app/assets/javascripts/discourse/components/topic-progress.js.es6
+++ b/app/assets/javascripts/discourse/components/topic-progress.js.es6
@@ -134,7 +134,9 @@ export default Ember.Component.extend({
       isDocked = offset >= threshold - windowHeight + topicProgressHeight + composerHeight;
     }
 
-    const dockPos = $(document).height() - $('#topic-footer-main-buttons').offset().top - topicProgressHeight;
+    const $mainButtons = $('#topic-footer-main-buttons');
+    const mainPos = $mainButtons.length > 0 ? $mainButtons.offset().top : 0;
+    const dockPos = $(document).height() - mainPos - topicProgressHeight;
 
     if (composerHeight > 0) {
       if (isDocked) {
diff --git a/app/assets/javascripts/discourse/controllers/topic.js.es6 b/app/assets/javascripts/discourse/controllers/topic.js.es6
index 5e6b0d3d8e7..0a56160bbcb 100644
--- a/app/assets/javascripts/discourse/controllers/topic.js.es6
+++ b/app/assets/javascripts/discourse/controllers/topic.js.es6
@@ -870,7 +870,7 @@ export default Ember.Controller.extend(SelectedPostsCount, BufferedContent, {
       }
 
       const max = _.max(postNumbers);
-      if (max > topic.get("last_read_post_number")) {
+      if (max > (topic.get("last_read_post_number") || 0)) {
         topic.set("last_read_post_number", max);
       }