diff --git a/js/src/forum/components/PostStreamScrubber.js b/js/src/forum/components/PostStreamScrubber.js
index 8395aba3c4..733db81227 100644
--- a/js/src/forum/components/PostStreamScrubber.js
+++ b/js/src/forum/components/PostStreamScrubber.js
@@ -198,6 +198,7 @@ export default class PostStreamScrubber extends Component {
     let index = $items.first().data('index') || 0;
     let visible = 0;
     let period = '';
+    let indexUpdated = false;
 
     // Now loop through each of the items in the discussion. An 'item' is
     // either a single post or a 'gap' of one or more posts that haven't
@@ -223,8 +224,9 @@ export default class PostStreamScrubber extends Component {
       const visibleBottom = Math.min(height, viewportTop + viewportHeight - top);
       const visiblePost = visibleBottom - visibleTop;
 
-      if (top <= viewportTop) {
+      if (!indexUpdated) {
         index = parseFloat($this.data('index')) + visibleTop / height;
+        indexUpdated = true;
       }
 
       if (visiblePost > 0) {