diff --git a/CHANGELOG.md b/CHANGELOG.md
index 49a16b22..b01d1fa3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,12 @@ FlatLaf Change Log
 - Popup: Fixed flicker of popups (e.g. tooltips) while they are moving (e.g.
   following mouse pointer). (issues #832 and #672)
 
+#### Fixed bugs
+
+- FlatLaf window decorations: Window top border on Windows 10 in "full window
+  content" mode was not fully repainted when activating or deactivating window.
+  (issue #809)
+
 #### Incompatibilities
 
 - ProgressBar: Log warning (including stack trace) when uninstalling
diff --git a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatTitlePane.java b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatTitlePane.java
index 7afcb8f7..181b7aeb 100644
--- a/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatTitlePane.java
+++ b/flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatTitlePane.java
@@ -222,7 +222,7 @@ public class FlatTitlePane
 			windowTopBorderLayer = new JPanel();
 			windowTopBorderLayer.setVisible( false );
 			windowTopBorderLayer.setOpaque( false );
-			windowTopBorderLayer.setBorder( FlatUIUtils.nonUIResource( FlatNativeWindowBorder.WindowTopBorder.getInstance() ) );
+			windowTopBorderLayer.setBorder( FlatUIUtils.nonUIResource( WindowTopBorder.getInstance() ) );
 		} else
 			windowTopBorderLayer = null;
 
@@ -745,16 +745,6 @@ public class FlatTitlePane
 		g.fillRect( 0, 0, getWidth(), getHeight() );
 	}
 
-	protected void repaintWindowBorder() {
-		int width = rootPane.getWidth();
-		int height = rootPane.getHeight();
-		Insets insets = rootPane.getInsets();
-		rootPane.repaint( 0, 0, width, insets.top ); // top
-		rootPane.repaint( 0, 0, insets.left, height ); // left
-		rootPane.repaint( 0, height - insets.bottom, width, insets.bottom ); // bottom
-		rootPane.repaint( width - insets.right, 0, insets.right, height ); // right
-	}
-
 	/**
 	 * Iconifies the window.
 	 */
@@ -1352,10 +1342,7 @@ public class FlatTitlePane
 			activeChanged( true );
 			updateNativeTitleBarHeightAndHitTestSpots();
 
-			if( isWindowTopBorderNeeded() )
-				WindowTopBorder.getInstance().repaintBorder( FlatTitlePane.this );
-
-			repaintWindowBorder();
+			repaintBorder();
 		}
 
 		@Override
@@ -1363,10 +1350,22 @@ public class FlatTitlePane
 			activeChanged( false );
 			updateNativeTitleBarHeightAndHitTestSpots();
 
-			if( isWindowTopBorderNeeded() )
+			repaintBorder();
+		}
+
+		private void repaintBorder() {
+			// Windows 10 top border
+			if( windowTopBorderLayer != null && windowTopBorderLayer.isShowing())
+				WindowTopBorder.getInstance().repaintBorder( windowTopBorderLayer );
+			else if( isWindowTopBorderNeeded() && !isWindowMaximized() && !isFullWindowContent() )
 				WindowTopBorder.getInstance().repaintBorder( FlatTitlePane.this );
 
-			repaintWindowBorder();
+			// Window border used for non-native window decorations
+			if( rootPane.getBorder() instanceof FlatRootPaneUI.FlatWindowBorder ) {
+				// not repainting four areas on the four sides because RepaintManager
+				// unions dirty regions, which also results in repaint of whole rootpane
+				rootPane.repaint();
+			}
 		}
 
 		@Override