diff --git a/app/assets/javascripts/discourse/app/lib/offset-calculator.js b/app/assets/javascripts/discourse/app/lib/offset-calculator.js
index c9cffee5cfd..9ce8c234e24 100644
--- a/app/assets/javascripts/discourse/app/lib/offset-calculator.js
+++ b/app/assets/javascripts/discourse/app/lib/offset-calculator.js
@@ -7,7 +7,14 @@ export function minimumOffset() {
     iPadNav = document.querySelector(".footer-nav-ipad .footer-nav"),
     iPadNavHeight = iPadNav ? iPadNav.offsetHeight : 0;
 
-  return header ? header.offsetHeight + iPadNavHeight : 0;
+  // if the header has a positive offset from the top of the window, we need to include the offset
+  // this covers cases where a site has a custom header above d-header (covers fixed and unfixed)
+  const headerWrap = document.querySelector(".d-header-wrap"),
+    headerWrapOffset = headerWrap.getBoundingClientRect();
+
+  return header
+    ? header.offsetHeight + headerWrapOffset.top + iPadNavHeight
+    : 0;
 }
 
 export default function offsetCalculator() {