diff --git a/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.cpp b/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.cpp
index be7ab21b268..7310b299983 100644
--- a/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.cpp
+++ b/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.cpp
@@ -26,4 +26,15 @@ String BackgroundSizeStyleValue::to_string(SerializationMode mode) const
     return MUST(String::formatted("{} {}", m_properties.size_x.to_string(mode), m_properties.size_y.to_string(mode)));
 }
 
+ValueComparingNonnullRefPtr<CSSStyleValue const> BackgroundSizeStyleValue::absolutized(CSSPixelRect const& viewport_rect, Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const
+{
+    auto absolutized_size_x = m_properties.size_x.absolutized(viewport_rect, font_metrics, root_font_metrics);
+    auto absolutized_size_y = m_properties.size_y.absolutized(viewport_rect, font_metrics, root_font_metrics);
+
+    if (absolutized_size_x == m_properties.size_x && absolutized_size_y == m_properties.size_y)
+        return *this;
+
+    return BackgroundSizeStyleValue::create(absolutized_size_x, absolutized_size_y);
+}
+
 }
diff --git a/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.h b/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.h
index 66a2164049f..2cba228c414 100644
--- a/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.h
+++ b/Libraries/LibWeb/CSS/StyleValues/BackgroundSizeStyleValue.h
@@ -28,6 +28,7 @@ public:
     LengthPercentage size_y() const { return m_properties.size_y; }
 
     virtual String to_string(SerializationMode) const override;
+    virtual ValueComparingNonnullRefPtr<CSSStyleValue const> absolutized(CSSPixelRect const& viewport_rect, Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const override;
 
     bool properties_equal(BackgroundSizeStyleValue const& other) const { return m_properties == other.m_properties; }
 
diff --git a/Tests/LibWeb/Text/expected/css/absolutized-background-size-value.txt b/Tests/LibWeb/Text/expected/css/absolutized-background-size-value.txt
index d61d2080de9..c13b5fc0e57 100644
--- a/Tests/LibWeb/Text/expected/css/absolutized-background-size-value.txt
+++ b/Tests/LibWeb/Text/expected/css/absolutized-background-size-value.txt
@@ -1 +1 @@
-calc(1em - 1px) calc(1em - 1px)
+15px 15px