diff --git a/Userland/Libraries/LibWeb/CSS/ComputedValues.h b/Userland/Libraries/LibWeb/CSS/ComputedValues.h
index 0989f731af..c5cef946e8 100644
--- a/Userland/Libraries/LibWeb/CSS/ComputedValues.h
+++ b/Userland/Libraries/LibWeb/CSS/ComputedValues.h
@@ -23,6 +23,7 @@ public:
     static CSS::TextAlign text_align() { return CSS::TextAlign::Left; }
     static CSS::Position position() { return CSS::Position::Static; }
     static CSS::TextDecorationLine text_decoration_line() { return CSS::TextDecorationLine::None; }
+    static CSS::Length text_decoration_thickness() { return Length::make_px(1); }
     static CSS::TextDecorationStyle text_decoration_style() { return CSS::TextDecorationStyle::Solid; }
     static CSS::TextTransform text_transform() { return CSS::TextTransform::None; }
     static CSS::Display display() { return CSS::Display { CSS::Display::Outside::Inline, CSS::Display::Inside::Flow }; }
@@ -111,6 +112,7 @@ public:
     Optional<int> const& z_index() const { return m_noninherited.z_index; }
     CSS::TextAlign text_align() const { return m_inherited.text_align; }
     CSS::TextDecorationLine text_decoration_line() const { return m_noninherited.text_decoration_line; }
+    CSS::LengthPercentage text_decoration_thickness() const { return m_noninherited.text_decoration_thickness; }
     CSS::TextDecorationStyle text_decoration_style() const { return m_noninherited.text_decoration_style; }
     Color text_decoration_color() const { return m_noninherited.text_decoration_color; }
     CSS::TextTransform text_transform() const { return m_inherited.text_transform; }
@@ -198,6 +200,7 @@ protected:
         CSS::Display display { InitialValues::display() };
         Optional<int> z_index;
         CSS::TextDecorationLine text_decoration_line { InitialValues::text_decoration_line() };
+        CSS::LengthPercentage text_decoration_thickness { InitialValues::text_decoration_thickness() };
         CSS::TextDecorationStyle text_decoration_style { InitialValues::text_decoration_style() };
         Color text_decoration_color { InitialValues::color() };
         CSS::Position position { InitialValues::position() };
@@ -257,6 +260,7 @@ public:
     void set_z_index(Optional<int> value) { m_noninherited.z_index = value; }
     void set_text_align(CSS::TextAlign text_align) { m_inherited.text_align = text_align; }
     void set_text_decoration_line(CSS::TextDecorationLine value) { m_noninherited.text_decoration_line = value; }
+    void set_text_decoration_thickness(CSS::LengthPercentage value) { m_noninherited.text_decoration_thickness = value; }
     void set_text_decoration_style(CSS::TextDecorationStyle value) { m_noninherited.text_decoration_style = value; }
     void set_text_decoration_color(Color value) { m_noninherited.text_decoration_color = value; }
     void set_text_transform(CSS::TextTransform value) { m_inherited.text_transform = value; }
diff --git a/Userland/Libraries/LibWeb/Layout/Node.cpp b/Userland/Libraries/LibWeb/Layout/Node.cpp
index c4fde9780a..768658fa57 100644
--- a/Userland/Libraries/LibWeb/Layout/Node.cpp
+++ b/Userland/Libraries/LibWeb/Layout/Node.cpp
@@ -430,6 +430,8 @@ void NodeWithStyle::apply_style(const CSS::StyleProperties& specified_style)
     //        we just manually grab the value from `color`. This makes it dependent on `color` being
     //        specified first, so it's far from ideal.
     computed_values.set_text_decoration_color(specified_style.color_or_fallback(CSS::PropertyID::TextDecorationColor, *this, computed_values.color()));
+    if (auto maybe_text_decoration_thickness = specified_style.length_percentage(CSS::PropertyID::TextDecorationThickness); maybe_text_decoration_thickness.has_value())
+        computed_values.set_text_decoration_thickness(maybe_text_decoration_thickness.release_value());
 
     computed_values.set_z_index(specified_style.z_index());
     computed_values.set_opacity(specified_style.opacity());
diff --git a/Userland/Libraries/LibWeb/Layout/TextNode.cpp b/Userland/Libraries/LibWeb/Layout/TextNode.cpp
index dfcdf7acda..4099c74450 100644
--- a/Userland/Libraries/LibWeb/Layout/TextNode.cpp
+++ b/Userland/Libraries/LibWeb/Layout/TextNode.cpp
@@ -70,17 +70,24 @@ void TextNode::paint_text_decoration(Gfx::Painter& painter, LineBoxFragment cons
 
     auto line_color = computed_values().text_decoration_color();
 
+    int line_thickness = [this] {
+        CSS::Length computed_thickness = computed_values().text_decoration_thickness().resolved(*this, CSS::Length(1, CSS::Length::Type::Em));
+        if (computed_thickness.is_auto())
+            return CSS::InitialValues::text_decoration_thickness().to_px(*this);
+
+        return computed_thickness.to_px(*this);
+    }();
+
     switch (computed_values().text_decoration_style()) {
         // FIXME: Implement the other styles
     case CSS::TextDecorationStyle::Solid:
     case CSS::TextDecorationStyle::Double:
     case CSS::TextDecorationStyle::Dashed:
     case CSS::TextDecorationStyle::Dotted:
-        painter.draw_line(line_start_point, line_end_point, line_color);
+        painter.draw_line(line_start_point, line_end_point, line_color, line_thickness);
         break;
     case CSS::TextDecorationStyle::Wavy:
-        // FIXME: There is a thing called text-decoration-thickness which also affects the amplitude here.
-        painter.draw_triangle_wave(line_start_point, line_end_point, line_color, 2);
+        painter.draw_triangle_wave(line_start_point, line_end_point, line_color, line_thickness + 1, line_thickness);
         break;
     }
 }