diff --git a/Libraries/LibWeb/CSS/StyleComputer.cpp b/Libraries/LibWeb/CSS/StyleComputer.cpp
index 0c9f1a32cc9..552ccbd8261 100644
--- a/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -1877,7 +1877,7 @@ RefPtr<Gfx::FontCascadeList const> StyleComputer::compute_font_for_style_values(
             auto length = value.as_length().length();
             if (length.is_absolute() || length.is_relative()) {
                 Length::FontMetrics font_metrics { font_size_in_px, font_pixel_metrics };
-                return length.to_px(viewport_rect(), font_metrics, m_root_element_font_metrics);
+                return length.to_px(viewport_rect(), font_metrics, root_element_font_metrics_for_element(element));
             }
         }
         return font_size_in_px;
@@ -1942,7 +1942,7 @@ RefPtr<Gfx::FontCascadeList const> StyleComputer::compute_font_for_style_values(
         Length::ResolutionContext const length_resolution_context {
             .viewport_rect = viewport_rect(),
             .font_metrics = Length::FontMetrics { parent_font_size, font_pixel_metrics },
-            .root_font_metrics = m_root_element_font_metrics,
+            .root_font_metrics = root_element_font_metrics_for_element(element),
         };
 
         Optional<Length> maybe_length;
@@ -2128,10 +2128,10 @@ Gfx::Font const& StyleComputer::initial_font() const
     return ComputedProperties::font_fallback(false, false, 12);
 }
 
-void StyleComputer::absolutize_values(ComputedProperties& style) const
+void StyleComputer::absolutize_values(ComputedProperties& style, GC::Ptr<DOM::Element const> element) const
 {
     Length::FontMetrics font_metrics {
-        m_root_element_font_metrics.font_size,
+        root_element_font_metrics_for_element(element).font_size,
         style.first_available_computed_font().pixel_metrics()
     };
 
@@ -2359,7 +2359,7 @@ GC::Ref<ComputedProperties> StyleComputer::create_document_style() const
     compute_math_depth(style, nullptr, {});
     compute_font(style, nullptr, {});
     compute_defaulted_values(style, nullptr, {});
-    absolutize_values(style);
+    absolutize_values(style, nullptr);
     style->set_property(CSS::PropertyID::Width, CSS::LengthStyleValue::create(CSS::Length::make_px(viewport_rect().width())));
     style->set_property(CSS::PropertyID::Height, CSS::LengthStyleValue::create(CSS::Length::make_px(viewport_rect().height())));
     style->set_property(CSS::PropertyID::Display, CSS::DisplayStyleValue::create(CSS::Display::from_short(CSS::Display::Short::Block)));
@@ -2644,7 +2644,7 @@ GC::Ref<ComputedProperties> StyleComputer::compute_properties(DOM::Element& elem
     compute_font(computed_style, &element, pseudo_element);
 
     // 4. Absolutize values, turning font/viewport relative lengths into absolute lengths
-    absolutize_values(computed_style);
+    absolutize_values(computed_style, element);
 
     // 5. Default the values, applying inheritance and 'initial' as needed
     compute_defaulted_values(computed_style, &element, pseudo_element);
@@ -3267,4 +3267,11 @@ void RuleCache::for_each_matching_rules(DOM::Element const& element, Optional<Se
     (void)callback(other_rules);
 }
 
+Length::FontMetrics const& StyleComputer::root_element_font_metrics_for_element(GC::Ptr<DOM::Element const> element) const
+{
+    if (element && element->document().document_element() == element)
+        return m_default_font_metrics;
+    return m_root_element_font_metrics;
+}
+
 }
diff --git a/Libraries/LibWeb/CSS/StyleComputer.h b/Libraries/LibWeb/CSS/StyleComputer.h
index fcedf1ccc3d..972114c664e 100644
--- a/Libraries/LibWeb/CSS/StyleComputer.h
+++ b/Libraries/LibWeb/CSS/StyleComputer.h
@@ -200,7 +200,7 @@ public:
 
     [[nodiscard]] GC::Ref<ComputedProperties> compute_properties(DOM::Element&, Optional<Selector::PseudoElement::Type>, CascadedProperties&) const;
 
-    void absolutize_values(ComputedProperties&) const;
+    void absolutize_values(ComputedProperties&, GC::Ptr<DOM::Element const>) const;
     void compute_font(ComputedProperties&, DOM::Element const*, Optional<CSS::Selector::PseudoElement::Type>) const;
 
     [[nodiscard]] inline bool should_reject_with_ancestor_filter(Selector const&) const;
@@ -303,6 +303,8 @@ private:
     using FontLoaderList = Vector<NonnullOwnPtr<FontLoader>>;
     HashMap<OwnFontFaceKey, FontLoaderList> m_loaded_fonts;
 
+    [[nodiscard]] Length::FontMetrics const& root_element_font_metrics_for_element(GC::Ptr<DOM::Element const>) const;
+
     Length::FontMetrics m_default_font_metrics;
     Length::FontMetrics m_root_element_font_metrics;
 
diff --git a/Libraries/LibWeb/DOM/Element.cpp b/Libraries/LibWeb/DOM/Element.cpp
index 6b719a19e3c..2c7b85805a7 100644
--- a/Libraries/LibWeb/DOM/Element.cpp
+++ b/Libraries/LibWeb/DOM/Element.cpp
@@ -631,7 +631,7 @@ CSS::RequiredInvalidationAfterStyleChange Element::recompute_inherited_style()
         return invalidation;
 
     document().style_computer().compute_font(*computed_properties, this, {});
-    document().style_computer().absolutize_values(*computed_properties);
+    document().style_computer().absolutize_values(*computed_properties, this);
 
     for (auto [property_id, old_value] : old_values_with_relative_units) {
         auto new_value = computed_properties->maybe_null_property(static_cast<CSS::PropertyID>(property_id));
diff --git a/Tests/LibWeb/Text/expected/css/font-size-rem-units-on-root-element.txt b/Tests/LibWeb/Text/expected/css/font-size-rem-units-on-root-element.txt
new file mode 100644
index 00000000000..61d49eff1e9
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/css/font-size-rem-units-on-root-element.txt
@@ -0,0 +1,4 @@
+68.6875px
+68.6875px
+68.6875px
+68.6875px
diff --git a/Tests/LibWeb/Text/input/css/font-size-rem-units-on-root-element.html b/Tests/LibWeb/Text/input/css/font-size-rem-units-on-root-element.html
new file mode 100644
index 00000000000..4a8d30c05b2
--- /dev/null
+++ b/Tests/LibWeb/Text/input/css/font-size-rem-units-on-root-element.html
@@ -0,0 +1,24 @@
+<style>
+:root { font-size: 1.1rem; }
+#whf { width: max-content; }
+</style>
+<body><div id="whf">WHF :^)</div></body>
+<script src="../include.js"></script>
+<script>
+    function relayout() {
+        let e = document.documentElement;
+        e.style.display = 'none';
+        e.style.display = '';
+        e.offsetWidth;
+    }
+    test(() => {
+        let cs = getComputedStyle(whf);
+        println(cs.width);
+        relayout();
+        println(cs.width);
+        relayout();
+        println(cs.width);
+        relayout();
+        println(cs.width);
+    });
+</script>