diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/util/SystemInfo.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/util/SystemInfo.java
index c96e804d..81cf4b41 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/util/SystemInfo.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/util/SystemInfo.java
@@ -113,9 +113,9 @@ public class SystemInfo
 
 		// features
 		// available since Java 12; backported to Java 11.0.8 and 8u292
-		isMacFullWindowContentSupported =
-			javaVersion >= toVersion( 11, 0, 8, 0 ) ||
-			(javaVersion >= toVersion( 1, 8, 0, 292 ) && !isJava_9_orLater);
+		isMacFullWindowContentSupported = isMacOS &&
+			(javaVersion >= toVersion( 11, 0, 8, 0 ) ||
+			 (javaVersion >= toVersion( 1, 8, 0, 292 ) && !isJava_9_orLater));
 
 
 		// Note: Keep following at the end of this block because (optional) loading
diff --git a/flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/FlatLafDemo.java b/flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/FlatLafDemo.java
index a0e4cd38..4a55f459 100644
--- a/flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/FlatLafDemo.java
+++ b/flatlaf-demo/src/main/java/com/formdev/flatlaf/demo/FlatLafDemo.java
@@ -55,7 +55,8 @@ public class FlatLafDemo
 			//   - "system": use current macOS appearance (light or dark)
 			//   - "NSAppearanceNameAqua": use light appearance
 			//   - "NSAppearanceNameDarkAqua": use dark appearance
-			// (needs to be set on main thread; setting it on AWT thread does not work)
+			// (must be set on main thread and before AWT/Swing is initialized;
+			//  setting it on AWT thread does not work)
 			System.setProperty( "apple.awt.application.appearance", "system" );
 		}
 
diff --git a/flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatLafThemeEditor.java b/flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatLafThemeEditor.java
index 110489ea..a2fd6792 100644
--- a/flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatLafThemeEditor.java
+++ b/flatlaf-theme-editor/src/main/java/com/formdev/flatlaf/themeeditor/FlatLafThemeEditor.java
@@ -41,7 +41,8 @@ public class FlatLafThemeEditor
 			//   - "system": use current macOS appearance (light or dark)
 			//   - "NSAppearanceNameAqua": use light appearance
 			//   - "NSAppearanceNameDarkAqua": use dark appearance
-			// (needs to be set on main thread; setting it on AWT thread does not work)
+			// (must be set on main thread and before AWT/Swing is initialized;
+			//  setting it on AWT thread does not work)
 			System.setProperty( "apple.awt.application.appearance", "system" );
 		}