diff --git a/CHANGELOG.md b/CHANGELOG.md
index db0ed487..c242393c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,14 @@
 FlatLaf Change Log
 ==================
 
+## 3.5.3-SNAPSHOT
+
+#### Fixed bugs
+
+- HTML: Fixed wrong rendering if HTML text contains `<style>` tag with
+  attributes (e.g. `<style type='text/css'>`). (issue #905; regression in 3.5.1)
+
+
 ## 3.5.2
 
 #### Fixed bugs
diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatHTML.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatHTML.java
index c8e23107..33173a5a 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatHTML.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatHTML.java
@@ -21,8 +21,8 @@ import java.beans.PropertyChangeEvent;
 import java.beans.PropertyChangeListener;
 import java.util.Arrays;
 import java.util.HashSet;
-import java.util.Locale;
 import java.util.Set;
+import java.util.function.BiConsumer;
 import javax.swing.AbstractButton;
 import javax.swing.JComponent;
 import javax.swing.JLabel;
@@ -93,7 +93,7 @@ debug*/
 			text = ((JToolTip)c).getTipText();
 		else
 			return;
-		if( text == null )
+		if( text == null || !BasicHTML.isHTMLString( text ) )
 			return;
 
 		// BASE_SIZE rule is parsed in javax.swing.text.html.StyleSheet.addRule()
@@ -101,15 +101,14 @@ debug*/
 		String openTag = "";
 		String closeTag = "";
 
-		String lowerText = text.toLowerCase( Locale.ENGLISH );
 		int headIndex;
 		int styleIndex;
 
 		int insertIndex;
-		if( (headIndex = lowerText.indexOf( "<head>" )) >= 0 ) {
+		if( (headIndex = indexOfTag( text, "head", true )) >= 0 ) {
 			// there is a <head> tag --> insert after <head> tag
-			insertIndex = headIndex + "<head>".length();
-		} else if( (styleIndex = lowerText.indexOf( "<style>" )) >= 0 ) {
+			insertIndex = headIndex;
+		} else if( (styleIndex = indexOfTag( text, "style", false )) >= 0 ) {
 			// there is a <style> tag --> insert before <style> tag
 			insertIndex = styleIndex;
 		} else {
@@ -124,6 +123,41 @@ debug*/
 			+ text.substring( insertIndex );
 
 		BasicHTML.updateRenderer( c, newText );
+
+		// for unit tests
+		if( testUpdateRenderer != null )
+			testUpdateRenderer.accept( c, newText );
+	}
+
+	// for unit tests
+	static BiConsumer<JComponent, String> testUpdateRenderer;
+
+	/**
+	 * Returns start or end index of a HTML tag.
+	 * Checks only for leading '<' character and (case-ignore) tag name.
+	 */
+	private static int indexOfTag( String html, String tag, boolean endIndex ) {
+		int tagLength = tag.length();
+		int maxLength = html.length() - tagLength - 2;
+		char lastTagChar = tag.charAt( tagLength - 1 );
+
+		for( int i = "<html>".length(); i < maxLength; i++ ) {
+			// check for leading '<' and last tag name character
+			if( html.charAt( i ) == '<' && Character.toLowerCase( html.charAt( i + tagLength ) ) == lastTagChar ) {
+				// compare tag characters from last to first
+				for( int j = tagLength - 2; j >= 0; j-- ) {
+					if( Character.toLowerCase( html.charAt( i + 1 + j ) ) != tag.charAt( j ) )
+						break; // not equal
+
+					if( j == 0 ) {
+						// tag found
+						return endIndex ? html.indexOf( '>', i + tagLength ) + 1 : i;
+					}
+				}
+			}
+		}
+
+		return -1;
 	}
 
 	private static final Set<String> absoluteSizeKeywordsSet = new HashSet<>( Arrays.asList(
diff --git a/flatlaf-core/src/test/java/com/formdev/flatlaf/ui/TestFlatHTML.java b/flatlaf-core/src/test/java/com/formdev/flatlaf/ui/TestFlatHTML.java
new file mode 100644
index 00000000..f6026112
--- /dev/null
+++ b/flatlaf-core/src/test/java/com/formdev/flatlaf/ui/TestFlatHTML.java
@@ -0,0 +1,113 @@
+/*
+ * Copyright 2024 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.formdev.flatlaf.ui;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import java.util.Locale;
+import javax.swing.JComponent;
+import javax.swing.JLabel;
+import javax.swing.UIManager;
+import javax.swing.plaf.basic.BasicHTML;
+import javax.swing.text.BadLocationException;
+import javax.swing.text.Document;
+import javax.swing.text.View;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Karl Tauber
+ */
+public class TestFlatHTML
+{
+	private final String body = "some <small>small</small> text";
+	private final String bodyInBody = "<body>" + body + "</body>";
+	private final String bodyPlain = "some small text";
+
+	@BeforeAll
+	static void setup() {
+		TestUtils.setup( false );
+		TestUtils.scaleFont( 2 );
+	}
+
+	@AfterAll
+	static void cleanup() {
+		TestUtils.cleanup();
+	}
+
+	@Test
+	void simple() {
+		testHtmlBaseSize( "<html>${BASE_SIZE_IN_HEAD}" + body + "</html>", bodyPlain );
+		testHtmlBaseSize( "<html>${BASE_SIZE_IN_HEAD}" + bodyInBody + "</html>", bodyPlain );
+	}
+
+	@Test
+	void htmlWithHeadTag() {
+		testHtmlBaseSize( "<html><head>${BASE_SIZE}<title>test</title><head>" + body + "</html>", bodyPlain );
+		testHtmlBaseSize( "<html><head>${BASE_SIZE}<title>test</title><head>" + bodyInBody + "</html>", bodyPlain );
+
+		testHtmlBaseSize( "<html><head id=\"abc\">${BASE_SIZE}<title>test</title><head>" + body + "</html>", bodyPlain );
+		testHtmlBaseSize( "<html><head id=\"abc\">${BASE_SIZE}<title>test</title><head>" + bodyInBody + "</html>", bodyPlain );
+	}
+
+	@Test
+	void htmlWithStyleTag() {
+		testHtmlBaseSize( "<html>${BASE_SIZE}<style>body { color: #f00; }</style>" + bodyInBody + "</html>", bodyPlain );
+		testHtmlBaseSize( "<html>${BASE_SIZE}<style>body { color: #f00; }</style><h1>header1</h1>" + body + "</html>", "header1\n" + bodyPlain );
+
+		testHtmlBaseSize( "<html>${BASE_SIZE}<style type='text/css'>body { color: #f00; }</style>" + bodyInBody + "</html>", bodyPlain );
+		testHtmlBaseSize( "<html>${BASE_SIZE}<style type='text/css'>body { color: #f00; }</style><h1>header1</h1>" + body + "</html>", "header1\n" + bodyPlain );
+	}
+
+	private void testHtmlBaseSize( String html, String expectedPlain ) {
+		testHtmlBaseSizeImpl( html, expectedPlain );
+		testHtmlBaseSizeImpl( html.toUpperCase( Locale.ENGLISH ), expectedPlain.toUpperCase( Locale.ENGLISH ) );
+	}
+
+	private void testHtmlBaseSizeImpl( String html, String expectedPlain ) {
+		String baseSize = "<style>BASE_SIZE " + UIManager.getFont( "Label.font" ).getSize() + "</style>";
+		String baseSizeInHead = "<head>" + baseSize + "</head>";
+
+		String expectedHtml = html.replace( "${BASE_SIZE}", baseSize ).replace( "${BASE_SIZE_IN_HEAD}", baseSizeInHead );
+		html = html.replace( "${BASE_SIZE}", "" ).replace( "${BASE_SIZE_IN_HEAD}", "" );
+
+		testHtml( html, expectedHtml, expectedPlain );
+	}
+
+	private void testHtml( String html, String expectedHtml, String expectedPlain ) {
+		FlatHTML.testUpdateRenderer = (c, newHtml) -> {
+			assertEquals( expectedHtml, newHtml );
+			assertEquals( expectedPlain, getPlainText( c ) );
+		};
+		new JLabel( html );
+		FlatHTML.testUpdateRenderer = null;
+	}
+
+	private String getPlainText( JComponent c ) {
+		View view = (View) c.getClientProperty( BasicHTML.propertyKey );
+		if( view == null )
+			return null;
+
+		Document doc = view.getDocument();
+		try {
+			return doc.getText( 0, doc.getLength() ).trim();
+		} catch( BadLocationException ex ) {
+			ex.printStackTrace();
+			return null;
+		}
+	}
+}
diff --git a/gradle.properties b/gradle.properties
index 45d95dee..3dbb0b31 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -15,7 +15,7 @@
 #
 
 flatlaf.releaseVersion     = 3.5.2
-flatlaf.developmentVersion = 3.6-SNAPSHOT
+flatlaf.developmentVersion = 3.5.3-SNAPSHOT
 
 org.gradle.parallel = true
 # org.gradle.warning.mode = all
