diff --git a/CHANGELOG.md b/CHANGELOG.md
index fc7efe32..ac966eb5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,9 @@ FlatLaf Change Log
   since FlatLaf 1.3)
 - OptionPane: Fixed `OptionPane.sameSizeButtons`, which did not work as expected
   when setting to `false`.
+- OptionPane: Fixed rendering of longer HTML text if it is passed as
+  `StringBuilder`, `StringBuffer`, or any other object that returns HTML text in
+  method `toString()`. (similar to issue #12)
 - TextField, FormattedTextField, PasswordField and ComboBox: Fixed alignment of
   placeholder text in right-to-left component orientation.
 
diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatOptionPaneUI.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatOptionPaneUI.java
index 2bb2c8f9..d0413691 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatOptionPaneUI.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatOptionPaneUI.java
@@ -24,6 +24,7 @@ import java.awt.GridBagConstraints;
 import java.awt.Insets;
 import javax.swing.Box;
 import javax.swing.BoxLayout;
+import javax.swing.Icon;
 import javax.swing.JComponent;
 import javax.swing.JLabel;
 import javax.swing.JPanel;
@@ -162,8 +163,15 @@ public class FlatOptionPaneUI
 			cons.insets.bottom = UIScale.scale( messagePadding );
 
 		// disable line wrapping for HTML
-		if( msg instanceof String && BasicHTML.isHTMLString( (String) msg ) )
-			maxll = Integer.MAX_VALUE;
+		if( msg != null &&
+			!(msg instanceof Component) &&
+			!(msg instanceof Object[]) &&
+			!(msg instanceof Icon) )
+		{
+			msg = msg.toString();
+			if( BasicHTML.isHTMLString( (String) msg ) )
+				maxll = Integer.MAX_VALUE;
+		}
 
 		// fix right-to-left alignment if super.addMessageComponents() breaks longer lines
 		// into multiple labels and puts them into a box that aligns them to the left