diff --git a/app/assets/javascripts/discourse/app/components/glimmer-site-header.gjs b/app/assets/javascripts/discourse/app/components/glimmer-site-header.gjs
index 72ba3d0b904..be18abe84cd 100644
--- a/app/assets/javascripts/discourse/app/components/glimmer-site-header.gjs
+++ b/app/assets/javascripts/discourse/app/components/glimmer-site-header.gjs
@@ -90,16 +90,28 @@ export default class GlimmerSiteHeader extends Component {
       return;
     }
 
-    // clamping to 0 to prevent negative values (hello, Safari)
-    const headerWrapBottom = Math.max(
+    // We expect this to be zero, but when overscrolling in Safari it can have a non-zero value:
+    const overscrollPx = Math.max(
       0,
-      Math.floor(this._headerWrap.getBoundingClientRect().bottom)
+      document.documentElement.getBoundingClientRect().top
     );
 
+    const headerWrapTop =
+      this._headerWrap.getBoundingClientRect().top - overscrollPx;
+    let headerWrapBottom =
+      this._headerWrap.getBoundingClientRect().bottom - overscrollPx;
+
+    // While scrolling on iOS, an element fixed to the top of the screen can have a `top` which fluctuates
+    // between -1 and 1. To avoid that fluctuation affecting the header offset, we subtract that tiny fluctuation from the bottom value.
+    if (Math.abs(headerWrapTop) < 1) {
+      headerWrapBottom -= headerWrapTop;
+    }
+
     let mainOutletOffsetTop = Math.max(
       0,
-      Math.floor(this._mainOutletWrapper.getBoundingClientRect().top) -
-        headerWrapBottom
+      this._mainOutletWrapper.getBoundingClientRect().top -
+        headerWrapBottom -
+        overscrollPx
     );
 
     if (DEBUG && isTesting()) {
@@ -111,16 +123,19 @@ export default class GlimmerSiteHeader extends Component {
     }
 
     const docStyle = document.documentElement.style;
+
     const currentHeaderOffset =
       parseInt(docStyle.getPropertyValue("--header-offset"), 10) || 0;
-    const newHeaderOffset = headerWrapBottom;
+    const newHeaderOffset = Math.floor(headerWrapBottom);
     if (currentHeaderOffset !== newHeaderOffset) {
       docStyle.setProperty("--header-offset", `${newHeaderOffset}px`);
     }
 
     const currentMainOutletOffset =
       parseInt(docStyle.getPropertyValue("--main-outlet-offset"), 10) || 0;
-    const newMainOutletOffset = headerWrapBottom + mainOutletOffsetTop;
+    const newMainOutletOffset = Math.floor(
+      headerWrapBottom + mainOutletOffsetTop
+    );
     if (currentMainOutletOffset !== newMainOutletOffset) {
       docStyle.setProperty("--main-outlet-offset", `${newMainOutletOffset}px`);
     }