diff --git a/CHANGELOG.md b/CHANGELOG.md
index 92cff378..c9f7a1a6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,12 +3,15 @@ FlatLaf Change Log
 
 ## 1.6.5-SNAPSHOT
 
+#### Fixed bugs
+
 - Linux: Fixed font problems when running on Oracle Java 8 (OpenJDK 8 is not
   affected):
   - oversized text if system font is "Inter" (issue #427)
   - missing text if system font is "Cantarell" (on Fedora)
 - MenuItem: Changed accelerator delimiter from `-` to `+`. (Windows and Linux).
-
+- ComboBox: Fixed occasional `StackOverflowError` when modifying combo box not
+  on AWT thread. (issue #432)
 
 ## 1.6.4
 
diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatComboBoxUI.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatComboBoxUI.java
index d991ee3a..8794c3d8 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatComboBoxUI.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatComboBoxUI.java
@@ -805,7 +805,9 @@ public class FlatComboBoxUI
 			this.padding = padding;
 		}
 
-		void install( Component c ) {
+		// using synchronized to avoid problems with code that modifies combo box
+		// (model, selection, etc) not on AWT thread (which should be not done)
+		synchronized void install( Component c ) {
 			if( !(c instanceof JComponent) )
 				return;
 
@@ -837,7 +839,7 @@ public class FlatComboBoxUI
 		 * there is no single place to uninstall it.
 		 * This is the reason why this method is called from various places.
 		 */
-		void uninstall() {
+		synchronized void uninstall() {
 			if( rendererComponent == null )
 				return;
 
@@ -848,9 +850,9 @@ public class FlatComboBoxUI
 		}
 
 		@Override
-		public Insets getBorderInsets( Component c, Insets insets ) {
+		synchronized public Insets getBorderInsets( Component c, Insets insets ) {
 			Insets padding = scale( this.padding );
-			if( rendererBorder != null ) {
+			if( rendererBorder != null && !(rendererBorder instanceof CellPaddingBorder) ) {
 				Insets insideInsets = rendererBorder.getBorderInsets( c );
 				insets.top = Math.max( padding.top, insideInsets.top );
 				insets.left = Math.max( padding.left, insideInsets.left );
diff --git a/flatlaf-testing/src/main/java/com/formdev/flatlaf/testing/FlatStressTest.java b/flatlaf-testing/src/main/java/com/formdev/flatlaf/testing/FlatStressTest.java
new file mode 100644
index 00000000..58b39a48
--- /dev/null
+++ b/flatlaf-testing/src/main/java/com/formdev/flatlaf/testing/FlatStressTest.java
@@ -0,0 +1,83 @@
+/*
+ * Copyright 2021 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.testing;
+
+import java.awt.Container;
+import java.awt.FlowLayout;
+import java.util.Random;
+import javax.swing.JComboBox;
+import javax.swing.JComponent;
+import javax.swing.JFrame;
+import javax.swing.SwingUtilities;
+import com.formdev.flatlaf.FlatClientProperties;
+import com.formdev.flatlaf.FlatLightLaf;
+
+/**
+ * @author Karl Tauber
+ */
+public class FlatStressTest
+{
+	public static void main( String[] args ) {
+		SwingUtilities.invokeLater( () -> {
+			FlatLightLaf.setup();
+			new FlatStressTest();
+		} );
+	}
+
+	protected FlatStressTest() {
+		JFrame frame = new JFrame( "FlatStressTest" );
+		frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
+
+		Container contentPane = frame.getContentPane();
+		contentPane.setLayout( new FlowLayout() );
+
+		contentPane.add( createStressTest() );
+
+		frame.setSize( 800, 600 );
+		frame.setLocationRelativeTo( null );
+		frame.setVisible( true );
+	}
+
+	private JComponent createStressTest() {
+		return createComboBoxStressTest();
+	}
+
+	// for https://github.com/JFormDesigner/FlatLaf/issues/432
+	// simulates StackOverflowError in FlatComboBoxUI when doing stuff in various threads
+	//
+	// requires adding `Thread.sleep( 1 );` to `FlatComboBoxUI.CellPaddingBorder.install()`
+	// after invocation of `uninstall()`
+	private JComponent createComboBoxStressTest() {
+		Random random = new Random();
+
+		JComboBox<String> comboBox = new JComboBox<>();
+		comboBox.putClientProperty( FlatClientProperties.MINIMUM_WIDTH, 0 );
+		for( int i = 0; i < 100; i++ )
+			comboBox.addItem( Integer.toString( random.nextInt() ) );
+
+		Thread thread = new Thread( () -> {
+			for(;;) {
+				comboBox.setSelectedIndex( random.nextInt( comboBox.getItemCount() ) );
+				comboBox.putClientProperty( FlatClientProperties.MINIMUM_WIDTH, random.nextInt( 500 ) );
+			}
+		});
+		thread.setDaemon( true );
+		thread.start();
+
+		return comboBox;
+	}
+}