diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
index dfbc04526b..d524c1b753 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -1832,21 +1832,14 @@ Optional<TimePercentage> Parser::parse_time_percentage(TokenStream<ComponentValu
     return {};
 }
 
-Optional<LengthOrCalculated> Parser::parse_source_size_value(ComponentValue const& component_value)
+Optional<LengthOrCalculated> Parser::parse_source_size_value(TokenStream<ComponentValue>& tokens)
 {
-    if (component_value.is_ident("auto"sv)) {
+    if (tokens.peek_token().is_ident("auto"sv)) {
+        (void)tokens.next_token(); // auto
         return LengthOrCalculated { Length::make_auto() };
     }
 
-    if (auto calculated_value = parse_calculated_value(component_value)) {
-        return LengthOrCalculated { calculated_value.release_nonnull() };
-    }
-
-    if (auto length = parse_length(component_value); length.has_value()) {
-        return LengthOrCalculated { length.release_value() };
-    }
-
-    return {};
+    return parse_length(tokens);
 }
 
 Optional<Length> Parser::parse_length(ComponentValue const& component_value)
@@ -6625,7 +6618,8 @@ LengthOrCalculated Parser::Parser::parse_as_sizes_attribute()
         //    let size be its value and remove the component value from unparsed size.
         //    FIXME: Any CSS function other than the math functions is invalid.
         //    Otherwise, there is a parse error; continue.
-        if (auto source_size_value = parse_source_size_value(unparsed_size.last()); source_size_value.has_value()) {
+        auto last_value_stream = TokenStream<ComponentValue>::of_single_token(unparsed_size.last());
+        if (auto source_size_value = parse_source_size_value(last_value_stream); source_size_value.has_value()) {
             size = source_size_value.value();
             unparsed_size.take_last();
         } else {
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
index e2ecfa0090..f04d318676 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.h
@@ -187,7 +187,7 @@ private:
     Optional<Color> parse_rgb_or_hsl_color(StringView function_name, Vector<ComponentValue> const&);
     Optional<Color> parse_color(ComponentValue const&);
     Optional<Length> parse_length(ComponentValue const&);
-    [[nodiscard]] Optional<LengthOrCalculated> parse_source_size_value(ComponentValue const&);
+    Optional<LengthOrCalculated> parse_source_size_value(TokenStream<ComponentValue>&);
     Optional<Ratio> parse_ratio(TokenStream<ComponentValue>&);
     Optional<Gfx::UnicodeRange> parse_unicode_range(TokenStream<ComponentValue>&);
     Optional<Gfx::UnicodeRange> parse_unicode_range(StringView);