diff --git a/Userland/Libraries/LibWeb/Layout/FormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/FormattingContext.cpp
index 554d331e7c..205aeb7734 100644
--- a/Userland/Libraries/LibWeb/Layout/FormattingContext.cpp
+++ b/Userland/Libraries/LibWeb/Layout/FormattingContext.cpp
@@ -345,11 +345,12 @@ float FormattingContext::compute_auto_height_for_block_formatting_context_root(L
     // whose bottom margin edge is below the element's bottom content edge,
     // then the height is increased to include those edges.
     for (auto* floating_box : state.get(root).floating_descendants()) {
-        auto const& floating_box_state = state.get(*floating_box);
-        float floating_box_bottom = floating_box_state.offset.y() + floating_box_state.content_height() + floating_box_state.margin_box_bottom();
-
-        if (!bottom.has_value() || floating_box_bottom > bottom.value())
-            bottom = floating_box_bottom;
+        // NOTE: Floating box coordinates are relative to their own containing block,
+        //       which may or may not be the BFC root.
+        auto margin_box = margin_box_rect_in_ancestor_coordinate_space(*floating_box, root, state);
+        float floating_box_bottom_margin_edge = margin_box.bottom() + 1;
+        if (!bottom.has_value() || floating_box_bottom_margin_edge > bottom.value())
+            bottom = floating_box_bottom_margin_edge;
     }
 
     return max(0.0f, bottom.value_or(0) - top.value_or(0));