diff --git a/bin/unit_tests/assets/html/ss64_deferred_cascade.css b/bin/unit_tests/assets/html/ss64_deferred_cascade.css
new file mode 100644
index 000000000..8fdbd76a7
--- /dev/null
+++ b/bin/unit_tests/assets/html/ss64_deferred_cascade.css
@@ -0,0 +1,11 @@
+h1 {
+  font-size: 1.5rem;
+}
+
+li a[href="../bash/"] {
+  background-color: #F8F9FA;
+}
+
+#external-css-loaded {
+  height: 37px;
+}
diff --git a/include/eepp/ui/css/stylesheet.hpp b/include/eepp/ui/css/stylesheet.hpp
index 2f17015cc..6ddd978bb 100644
--- a/include/eepp/ui/css/stylesheet.hpp
+++ b/include/eepp/ui/css/stylesheet.hpp
@@ -11,6 +11,8 @@ namespace EE { namespace UI { namespace CSS {
 
 class EE_API StyleSheet {
   public:
+	using SourceOrder = Uint32;
+
 	StyleSheet();
 
 	void clear();
@@ -23,6 +25,10 @@ class EE_API StyleSheet {
 
 	void combineStyleSheet( const StyleSheet& styleSheet );
 
+	void combineStyleSheet( const StyleSheet& styleSheet, SourceOrder sourceOrder );
+
+	SourceOrder reserveSourceOrder();
+
 	std::shared_ptr<ElementDefinition> getElementStyles( UIWidget* element,
 														 const bool& applyPseudo = false ) const;
 
@@ -78,6 +84,18 @@ class EE_API StyleSheet {
 	StyleSheet& operator=( const StyleSheet& other );
 
   protected:
+	struct SourcePosition {
+		SourceOrder styleSheet{ 0 };
+		Uint32 rule{ 0 };
+
+		bool operator<( const SourcePosition& other ) const {
+			if ( styleSheet != other.styleSheet )
+				return styleSheet < other.styleSheet;
+			return rule < other.rule;
+		}
+	};
+	static_assert( sizeof( SourcePosition ) == sizeof( Uint64 ) );
+
 	Uint64 mVersion{ 1 };
 	Uint32 mMarker{ 0 };
 	std::vector<std::shared_ptr<StyleSheetStyle>> mNodes;
@@ -87,8 +105,8 @@ class EE_API StyleSheet {
 	UnorderedMap<String::HashType, StyleSheetStyleVector> mClassNodeIndex;
 	// Candidate buckets are independent, so retain insertion order explicitly for equal
 	// specificity.
-	UnorderedMap<const StyleSheetStyle*, size_t> mStyleSourceOrder;
-	size_t mNextStyleSourceOrder{ 0 };
+	UnorderedMap<const StyleSheetStyle*, SourcePosition> mStyleSourceOrder;
+	SourceOrder mNextStyleSourceOrder{ 0 };
 	MediaQueryList::vector mMediaQueryList;
 	KeyframesDefinitionMap mKeyframesMap;
 	using ElementDefinitionCache = UnorderedMap<size_t, std::shared_ptr<ElementDefinition>>;
@@ -99,6 +117,9 @@ class EE_API StyleSheet {
 	void addMediaQueryList( MediaQueryList::ptr list );
 
 	bool addStyleToNodeIndex( StyleSheetStyle* style );
+
+	void addStyle( std::shared_ptr<StyleSheetStyle> node, SourceOrder sourceOrder,
+				   Uint32 ruleOrder );
 };
 
 }}} // namespace EE::UI::CSS
diff --git a/include/eepp/ui/uiscenenode.hpp b/include/eepp/ui/uiscenenode.hpp
index 0d7454952..65229c3dd 100644
--- a/include/eepp/ui/uiscenenode.hpp
+++ b/include/eepp/ui/uiscenenode.hpp
@@ -407,9 +407,11 @@ class EE_API UISceneNode : public SceneNode {
 	 * @param forceReloadStyle If true, forces immediate style reload (default: true).
 	 * @param baseURI If the resource was loaded from an URI, pass the URI in order to solve
 	 * relative paths in CSS
+	 * @param sourceOrder Reserved document order for a stylesheet loaded asynchronously.
 	 */
 	void combineStyleSheet( const CSS::StyleSheet& styleSheet, bool forceReloadStyle = true,
-							URI baseURI = {} );
+							URI baseURI = {},
+							std::optional<CSS::StyleSheet::SourceOrder> sourceOrder = {} );
 
 	/**
 	 * @brief Combines an inline stylesheet with the existing one.
@@ -421,9 +423,11 @@ class EE_API UISceneNode : public SceneNode {
 	 * @param marker Marker to associate with the new styles.
 	 * @param baseURI If the resource was loaded from an URI, pass the URI in order to solve
 	 * relative paths in CSS
+	 * @param sourceOrder Reserved document order for a stylesheet loaded asynchronously.
 	 */
 	void combineStyleSheet( const std::string& inlineStyleSheet, bool forceReloadStyle = true,
-							const Uint32& marker = 0, URI baseURI = {} );
+							const Uint32& marker = 0, URI baseURI = {},
+							std::optional<CSS::StyleSheet::SourceOrder> sourceOrder = {} );
 
 	/**
 	 * @brief Gets the reference to the current stylesheet.
@@ -1161,8 +1165,9 @@ class EE_API UISceneNode : public SceneNode {
 	 *
 	 * @param uri URI to load
 	 * @param defer Defer some specific time the CSS load (0 to just load it asynchronously)
+	 * @param sourceOrder Document order reserved when the stylesheet link was encountered.
 	 */
-	void loadCSS( URI uri, std::optional<Time> defer = {} );
+	void loadCSS( URI uri, std::optional<Time> defer, CSS::StyleSheet::SourceOrder sourceOrder );
 
 	/**
 	 * @brief Loads glyph icons from @glyph-icon rules.
diff --git a/src/eepp/ui/css/stylesheet.cpp b/src/eepp/ui/css/stylesheet.cpp
index f7d931e9e..99d99eb1b 100644
--- a/src/eepp/ui/css/stylesheet.cpp
+++ b/src/eepp/ui/css/stylesheet.cpp
@@ -120,21 +120,25 @@ void StyleSheet::setSelectorSpecificity( const Int64& specificity ) {
 
 StyleSheet StyleSheet::getAllWithMarker( const Uint32& marker ) const {
 	StyleSheet style;
-	std::vector<std::shared_ptr<StyleSheetStyle>> hits;
 	for ( auto node : mNodes ) {
-		if ( node->getMarker() == marker )
-			style.addStyle( node );
+		if ( node->getMarker() == marker ) {
+			const SourcePosition& position = mStyleSourceOrder.at( node.get() );
+			style.addStyle( node, position.styleSheet, position.rule );
+		}
 	}
+	style.mNextStyleSourceOrder = mNextStyleSourceOrder;
 	return style;
 }
 
 StyleSheet StyleSheet::getAllWithMarkers() const {
 	StyleSheet style;
-	std::vector<std::shared_ptr<StyleSheetStyle>> hits;
 	for ( auto node : mNodes ) {
-		if ( node->getMarker() != 0 )
-			style.addStyle( node );
+		if ( node->getMarker() != 0 ) {
+			const SourcePosition& position = mStyleSourceOrder.at( node.get() );
+			style.addStyle( node, position.styleSheet, position.rule );
+		}
 	}
+	style.mNextStyleSourceOrder = mNextStyleSourceOrder;
 	return style;
 }
 
@@ -225,14 +229,23 @@ bool StyleSheet::addStyleToNodeIndex( StyleSheetStyle* style ) {
 }
 
 void StyleSheet::addStyle( std::shared_ptr<StyleSheetStyle> node ) {
+	addStyle( std::move( node ), reserveSourceOrder(), 0 );
+}
+
+void StyleSheet::addStyle( std::shared_ptr<StyleSheetStyle> node, SourceOrder sourceOrder,
+						   Uint32 ruleOrder ) {
 	if ( addStyleToNodeIndex( node.get() ) ) {
-		mStyleSourceOrder[node.get()] = mNextStyleSourceOrder++;
+		mStyleSourceOrder[node.get()] = { sourceOrder, ruleOrder };
 		mNodes.push_back( node );
 	}
 	addMediaQueryList( node->getMediaQueryList() );
 	mVersion++;
 }
 
+StyleSheet::SourceOrder StyleSheet::reserveSourceOrder() {
+	return mNextStyleSourceOrder++;
+}
+
 bool StyleSheet::isEmpty() const {
 	return mNodes.empty();
 }
@@ -259,9 +272,13 @@ std::string StyleSheet::print() {
 }
 
 void StyleSheet::combineStyleSheet( const StyleSheet& styleSheet ) {
-	for ( auto& style : styleSheet.getStyles() ) {
-		addStyle( style );
-	}
+	combineStyleSheet( styleSheet, reserveSourceOrder() );
+}
+
+void StyleSheet::combineStyleSheet( const StyleSheet& styleSheet, SourceOrder sourceOrder ) {
+	Uint32 ruleOrder = 0;
+	for ( auto& style : styleSheet.getStyles() )
+		addStyle( style, sourceOrder, ruleOrder++ );
 
 	addKeyframes( styleSheet.getKeyframes() );
 }
diff --git a/src/eepp/ui/uiscenenode.cpp b/src/eepp/ui/uiscenenode.cpp
index 3c44514b0..3eede34de 100644
--- a/src/eepp/ui/uiscenenode.cpp
+++ b/src/eepp/ui/uiscenenode.cpp
@@ -552,7 +552,8 @@ std::vector<UIWidget*> UISceneNode::loadNode( pugi::xml_node node, Node* parent,
 			if ( !href.empty() &&
 				 ( String::iequals( type.value(), "text/css" ) ||
 				   String::icontains( std::string_view{ rel.value() }, "stylesheet" ) ) ) {
-				loadCSS( href.as_string(), Milliseconds( defer.as_int() ) );
+				loadCSS( href.as_string(), Milliseconds( defer.as_int() ),
+						 mStyleSheet.reserveSourceOrder() );
 			}
 			continue;
 		} else if ( String::iequals( widget.name(), "meta" ) ) {
@@ -703,8 +704,10 @@ void UISceneNode::updateStyleSheet( bool forceReloadStyle ) {
 }
 
 void UISceneNode::combineStyleSheet( const CSS::StyleSheet& styleSheet, bool forceReloadStyle,
-									 URI baseURI ) {
-	mStyleSheet.combineStyleSheet( styleSheet );
+									 URI baseURI,
+									 std::optional<CSS::StyleSheet::SourceOrder> sourceOrder ) {
+	mStyleSheet.combineStyleSheet( styleSheet,
+								   sourceOrder ? *sourceOrder : mStyleSheet.reserveSourceOrder() );
 
 	processStyleSheetAtRules( styleSheet, baseURI );
 
@@ -719,14 +722,15 @@ void UISceneNode::combineStyleSheet( const CSS::StyleSheet& styleSheet, bool for
 }
 
 void UISceneNode::combineStyleSheet( const std::string& inlineStyleSheet, bool forceReloadStyle,
-									 const Uint32& marker, URI baseURI ) {
+									 const Uint32& marker, URI baseURI,
+									 std::optional<CSS::StyleSheet::SourceOrder> sourceOrder ) {
 	CSS::StyleSheetParser parser;
 	parser.setBaseURI( baseURI );
 
 	if ( parser.loadFromString( inlineStyleSheet ) ) {
 		parser.getStyleSheet().setMarker( marker );
 		resolveStyleSheetRelativeURLs( parser.getStyleSheet(), baseURI.empty() ? mURI : baseURI );
-		combineStyleSheet( parser.getStyleSheet(), forceReloadStyle, baseURI );
+		combineStyleSheet( parser.getStyleSheet(), forceReloadStyle, baseURI, sourceOrder );
 	}
 }
 
@@ -1857,7 +1861,8 @@ URI UISceneNode::solveRelativePath( URI uri, URI baseURI ) {
 	return base;
 }
 
-void UISceneNode::loadCSS( URI uri, std::optional<Time> defer ) {
+void UISceneNode::loadCSS( URI uri, std::optional<Time> defer,
+						   CSS::StyleSheet::SourceOrder sourceOrder ) {
 	uri = solveRelativePath( uri );
 	std::string url = uri.toString();
 	Log::debug( "UISceneNode::loadCSS: %s", url );
@@ -1869,7 +1874,7 @@ void UISceneNode::loadCSS( URI uri, std::optional<Time> defer ) {
 			Uint64 resourceGeneration =
 				resourceState ? resourceState->generation.load( std::memory_order_acquire ) : 0;
 			URI baseURL = getURIFromURL( url );
-			mThreadPool->run( [resourceState, resourceGeneration, uri, url, defer,
+			mThreadPool->run( [resourceState, resourceGeneration, uri, url, defer, sourceOrder,
 							   baseURL = std::move( baseURL )] {
 				Clock c;
 				std::string filePath( uri.getFSPath() );
@@ -1883,9 +1888,10 @@ void UISceneNode::loadCSS( URI uri, std::optional<Time> defer ) {
 							delay = Time::Zero;
 						UISceneNode::runAsyncResourceOnMainThread(
 							resourceState, resourceGeneration,
-							[url, baseURL,
+							[url, baseURL, sourceOrder,
 							 parser = std::move( parser )]( UISceneNode* scene ) mutable {
-								scene->combineStyleSheet( parser.getStyleSheet(), true, baseURL );
+								scene->combineStyleSheet( parser.getStyleSheet(), true, baseURL,
+														  sourceOrder );
 								Log::debug( "UISceneNode::loadCSS: Loaded - %s", url );
 							},
 							delay );
@@ -1896,7 +1902,8 @@ void UISceneNode::loadCSS( URI uri, std::optional<Time> defer ) {
 			std::string filePath( uri.getFSPath() );
 			std::string css;
 			if ( FileSystem::fileExists( filePath ) && FileSystem::fileGet( filePath, css ) ) {
-				combineStyleSheet( css, true, String::hash( url ), getURIFromURL( url ) );
+				combineStyleSheet( css, true, String::hash( url ), getURIFromURL( url ),
+								   sourceOrder );
 				Log::debug( "UISceneNode::loadCSS: Loaded - %s", url );
 			}
 		}
@@ -1910,7 +1917,7 @@ void UISceneNode::loadCSS( URI uri, std::optional<Time> defer ) {
 		request.kind = WebResourceKind::StyleSheet;
 		request.timeout = Seconds( 5 );
 		requestWebResource( std::move( request ), [resourceState, resourceGeneration, url,
-												   baseURL = std::move( baseURL )](
+												   sourceOrder, baseURL = std::move( baseURL )](
 													  const WebResourceResult& result ) {
 			if ( !UISceneNode::isAsyncResourceLoadCurrent( resourceState, resourceGeneration ) )
 				return;
@@ -1918,8 +1925,10 @@ void UISceneNode::loadCSS( URI uri, std::optional<Time> defer ) {
 				std::string css( *result.data );
 				UISceneNode::runAsyncResourceOnMainThread(
 					resourceState, resourceGeneration,
-					[css = std::move( css ), url, baseURL]( UISceneNode* scene ) mutable {
-						scene->combineStyleSheet( css, true, String::hash( url ), baseURL );
+					[css = std::move( css ), url, baseURL,
+					 sourceOrder]( UISceneNode* scene ) mutable {
+						scene->combineStyleSheet( css, true, String::hash( url ), baseURL,
+												  sourceOrder );
 						Log::debug( "UISceneNode::loadCSS: Loaded - %s", url );
 					} );
 			} else {
@@ -1931,7 +1940,7 @@ void UISceneNode::loadCSS( URI uri, std::optional<Time> defer ) {
 		CSS::StyleSheetParser parser;
 		if ( parser.loadFromStream( *stream ) ) {
 			parser.getStyleSheet().setMarker( String::hash( url ) );
-			combineStyleSheet( parser.getStyleSheet() );
+			combineStyleSheet( parser.getStyleSheet(), true, {}, sourceOrder );
 			Log::debug( "UISceneNode::loadCSS: Loaded - %s", url );
 		}
 	} else {
diff --git a/src/tests/unit_tests/uihtml_float_tests.cpp b/src/tests/unit_tests/uihtml_float_tests.cpp
index ad1cdf699..937a176d7 100644
--- a/src/tests/unit_tests/uihtml_float_tests.cpp
+++ b/src/tests/unit_tests/uihtml_float_tests.cpp
@@ -703,6 +703,50 @@ UTEST( UIHTMLFloat, ss64NarrowViewportFloatsDoNotOverlapAtPixelDensity1 ) {
 	Engine::destroySingleton();
 }
 
+UTEST( UIHTMLFloat, ss64DeferredStyleSheetPreservesDocumentSourceOrder ) {
+	init_float_test();
+	UISceneNode* sceneNode = SceneManager::instance()->getUISceneNode();
+	sceneNode->setThreadPool( ThreadPool::createShared( 1 ) );
+	sceneNode->setURI( "file://" + Sys::getProcessPath() + "assets/html/" );
+
+	sceneNode->loadLayoutFromString( HTMLFormatter::HTMLtoXML( R"html(
+		<html>
+		<head>
+			<link rel="stylesheet" href="ss64_deferred_cascade.css" defer="25" />
+			<style>
+				h1 { font-size: 1rem; }
+				li a[href="../bash/"] { background-color: #FFCC33; }
+			</style>
+		</head>
+		<body>
+			<div id="external-css-loaded"></div>
+			<h1 id="heading">Command line reference.</h1>
+			<ul><li><a id="linux" href="../bash/">Linux</a></li></ul>
+		</body>
+		</html>
+	)html" ) );
+
+	auto* heading = sceneNode->getRoot()->find( "heading" )->asType<UIRichText>();
+	auto* linux = sceneNode->getRoot()->find( "linux" )->asType<UIRichText>();
+	auto* loaded = sceneNode->getRoot()->find( "external-css-loaded" )->asType<UIWidget>();
+	ASSERT_TRUE( heading != nullptr );
+	ASSERT_TRUE( linux != nullptr );
+	ASSERT_TRUE( loaded != nullptr );
+	const Uint32 inlineHeadingFontSize = heading->getFontSize();
+	const Color inlineLinuxBackground = linux->getBackgroundColor();
+
+	for ( int i = 0; i < 500 && loaded->getPixelsSize().getHeight() < 36.f; ++i ) {
+		SceneManager::instance()->update();
+		Sys::sleep( Milliseconds( 1 ) );
+	}
+
+	ASSERT_NEAR( loaded->getPixelsSize().getHeight(), 37.f, 1.f );
+	EXPECT_EQ( heading->getFontSize(), inlineHeadingFontSize );
+	EXPECT_TRUE( linux->getBackgroundColor() == inlineLinuxBackground );
+
+	Engine::destroySingleton();
+}
+
 UTEST( UIHTMLFloat, autoHorizontalMarginsCenterBlockInsideFloat ) {
 	init_float_test();
 	UISceneNode* sceneNode = SceneManager::instance()->getUISceneNode();