diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
index a0d9da7371..91bbaad40f 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -1503,7 +1503,12 @@ Optional<Length> Parser::parse_length(ParsingContext const& context, StyleCompon
 
 RefPtr<StyleValue> Parser::parse_length_value(ParsingContext const& context, StyleComponentValueRule const& component_value)
 {
-    if (component_value.is(Token::Type::Dimension) || component_value.is(Token::Type::Number) || component_value.is(Token::Type::Percentage)) {
+    // Numbers with no units can be lengths, in two situations:
+    // 1) We're in quirks mode, and it's an integer.
+    // 2) It's a 0.
+    // We handle case 1 here. Case 2 is handled by NumericStyleValue pretending to be a LengthStyleValue if it is 0.
+    if (component_value.is(Token::Type::Dimension) || component_value.is(Token::Type::Percentage)
+        || (context.in_quirks_mode() && component_value.is(Token::Type::Number) && component_value.token().m_value.string_view() != "0"sv)) {
         auto length = parse_length(context, component_value);
         if (length.has_value())
             return LengthStyleValue::create(length.value());
diff --git a/Userland/Libraries/LibWeb/CSS/StyleProperties.cpp b/Userland/Libraries/LibWeb/CSS/StyleProperties.cpp
index caefdc203e..b066a96e8b 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleProperties.cpp
+++ b/Userland/Libraries/LibWeb/CSS/StyleProperties.cpp
@@ -299,12 +299,13 @@ Optional<float> StyleProperties::flex_grow_factor() const
     auto value = property(CSS::PropertyID::FlexGrow);
     if (!value.has_value())
         return {};
-    if (value.value()->is_length() && verify_cast<CSS::LengthStyleValue>(value.value().ptr())->to_length().raw_value() == 0)
+    if (value.value()->is_numeric()) {
+        auto numeric = verify_cast<CSS::NumericStyleValue>(value.value().ptr());
+        return numeric->value();
+    }
+    if (value.value()->is_length() && value.value()->to_length().raw_value() == 0)
         return { 0 };
-    if (!value.value()->is_numeric())
-        return {};
-    auto numeric = verify_cast<CSS::NumericStyleValue>(value.value().ptr());
-    return numeric->value();
+    return {};
 }
 
 Optional<float> StyleProperties::flex_shrink_factor() const
@@ -312,12 +313,13 @@ Optional<float> StyleProperties::flex_shrink_factor() const
     auto value = property(CSS::PropertyID::FlexShrink);
     if (!value.has_value())
         return {};
-    if (value.value()->is_length() && verify_cast<CSS::LengthStyleValue>(value.value().ptr())->to_length().raw_value() == 0)
+    if (!value.value()->is_numeric()) {
+        auto numeric = verify_cast<CSS::NumericStyleValue>(value.value().ptr());
+        return numeric->value();
+    }
+    if (value.value()->is_length() && value.value()->to_length().raw_value() == 0)
         return { 0 };
-    if (!value.value()->is_numeric())
-        return {};
-    auto numeric = verify_cast<CSS::NumericStyleValue>(value.value().ptr());
-    return numeric->value();
+    return {};
 }
 Optional<CSS::JustifyContent> StyleProperties::justify_content() const
 {
diff --git a/Userland/Libraries/LibWeb/CSS/StyleValue.h b/Userland/Libraries/LibWeb/CSS/StyleValue.h
index 9fd8019e6d..8790379ee7 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleValue.h
+++ b/Userland/Libraries/LibWeb/CSS/StyleValue.h
@@ -239,7 +239,7 @@ public:
     bool is_identifier() const { return type() == Type::Identifier; }
     bool is_image() const { return type() == Type::Image; }
     bool is_string() const { return type() == Type::String; }
-    bool is_length() const { return type() == Type::Length; }
+    virtual bool is_length() const { return type() == Type::Length; }
     bool is_custom_property() const { return type() == Type::CustomProperty; }
     bool is_numeric() const { return type() == Type::Numeric; }
     bool is_value_list() const { return type() == Type::ValueList; }
@@ -303,6 +303,9 @@ public:
         return adopt_ref(*new NumericStyleValue(value));
     }
 
+    virtual bool is_length() const override { return m_value == 0; }
+    virtual Length to_length() const override { return Length(0, Length::Type::Px); }
+
     float value() const { return m_value; }
     String to_string() const override { return String::formatted("{}", m_value); }