diff --git a/app/assets/javascripts/discourse/lib/offset-calculator.js.es6 b/app/assets/javascripts/discourse/lib/offset-calculator.js.es6
index 3c2fc1fc71..81e97e97dd 100644
--- a/app/assets/javascripts/discourse/lib/offset-calculator.js.es6
+++ b/app/assets/javascripts/discourse/lib/offset-calculator.js.es6
@@ -36,8 +36,12 @@ export default function offsetCalculator(y) {
   if (inter > ideal) {
     const bottom = $('#topic-bottom').offset().top;
     const switchPos = bottom - rawWinHeight;
+    if (scrollPercent >= 1.0) {
+      return 0;
+    }
+
     if (scrollTop > switchPos) {
-      const p = Math.max(Math.min((scrollTop + inter - switchPos) / bottom, 1.0), 0.0);
+      const p = Math.max(Math.min((scrollTop + inter - switchPos) / rawWinHeight, 1.0), 0.0);
       return ((1 - p) * ideal) + (p * inter);
     } else {
       return ideal;