Index: class/Managed.Windows.Forms/System.Windows.Forms/Theme.cs
===================================================================
--- class/Managed.Windows.Forms/System.Windows.Forms/Theme.cs	(revision 104790)
+++ class/Managed.Windows.Forms/System.Windows.Forms/Theme.cs	(working copy)
@@ -532,7 +532,7 @@
 
 		public virtual Size ToolWindowCaptionButtonSize {
 			get {
-				return new Size(15, 15);
+				return XplatUI.ToolWindowCaptionButtonSize;
 			}
 		}
 
Index: class/Managed.Windows.Forms/System.Windows.Forms/XplatUI.cs
===================================================================
--- class/Managed.Windows.Forms/System.Windows.Forms/XplatUI.cs	(revision 104790)
+++ class/Managed.Windows.Forms/System.Windows.Forms/XplatUI.cs	(working copy)
@@ -412,6 +412,12 @@
 			}
 		}
 
+		public static Size ToolWindowCaptionButtonSize {
+			get {
+				return driver.ToolWindowCaptionButtonSize;
+			}
+		}
+
 		#endregion	// Public Static Properties
 
 		#region Events
Index: class/Managed.Windows.Forms/System.Windows.Forms/XplatUIDriver.cs
===================================================================
--- class/Managed.Windows.Forms/System.Windows.Forms/XplatUIDriver.cs	(revision 104790)
+++ class/Managed.Windows.Forms/System.Windows.Forms/XplatUIDriver.cs	(working copy)
@@ -242,6 +242,12 @@
 		internal abstract Rectangle WorkingArea { get; }
 		internal abstract bool ThemesEnabled { get; }
 
+		internal virtual Size ToolWindowCaptionButtonSize {
+			get {
+				return new Size (15, 15);
+			}
+		}
+
 		#endregion	// XplatUI Driver Properties
 
 		internal abstract event EventHandler Idle;
Index: class/Managed.Windows.Forms/System.Windows.Forms/XplatUIWin32.cs
===================================================================
--- class/Managed.Windows.Forms/System.Windows.Forms/XplatUIWin32.cs	(revision 104790)
+++ class/Managed.Windows.Forms/System.Windows.Forms/XplatUIWin32.cs	(working copy)
@@ -1506,6 +1506,14 @@
 				return XplatUIWin32.themes_enabled;
 			}
 		}
+
+		internal override Size ToolWindowCaptionButtonSize {
+			get {
+				return new Size (
+					Win32GetSystemMetrics (SystemMetrics.SM_CXSMSIZE),
+					Win32GetSystemMetrics (SystemMetrics.SM_CYSMSIZE));
+			}
+		}
  
 
 		#endregion	// Static Properties