diff --git a/src/Avalonia.Controls/ComboBox.cs b/src/Avalonia.Controls/ComboBox.cs
index fc7feca7f1..5ba1195159 100644
--- a/src/Avalonia.Controls/ComboBox.cs
+++ b/src/Avalonia.Controls/ComboBox.cs
@@ -432,11 +432,11 @@ namespace Avalonia.Controls
 
         private void UpdateFlowDirection()
         {
-            var rectangle = SelectionBoxItem as Rectangle;
-            if (rectangle != null)
+            if (SelectionBoxItem is Rectangle rectangle)
             {
                 var content = (rectangle.Fill as VisualBrush)!.Visual as Control;
-                var flowDirection = (((IVisual)content!).VisualParent as Control)?.FlowDirection ?? FlowDirection.LeftToRight;
+                var flowDirection = (((IVisual)content!).VisualParent as Control)?.FlowDirection ?? 
+                    FlowDirection.LeftToRight;
 
                 rectangle.FlowDirection = flowDirection;
             }
diff --git a/tests/Avalonia.Controls.UnitTests/ComboBoxTests.cs b/tests/Avalonia.Controls.UnitTests/ComboBoxTests.cs
index 0804de3174..70b713d6d0 100644
--- a/tests/Avalonia.Controls.UnitTests/ComboBoxTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ComboBoxTests.cs
@@ -8,7 +8,7 @@ using Avalonia.Data;
 using Avalonia.Input;
 using Avalonia.LogicalTree;
 using Avalonia.Media;
-using Avalonia.Threading;
+using Avalonia.VisualTree;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -340,80 +340,77 @@ namespace Avalonia.Controls.UnitTests
         [Fact]
         public void FlowDirection_Of_RectangleContent_Shuold_Be_LeftToRight()
         {
-            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            var items = new[]
             {
-                var items = new[]
-                {
-                    new ComboBoxItem()
-                    { 
-                        Content = new Control()
-                    }
-                };
-                var target = new ComboBox
-                {
-                    FlowDirection = FlowDirection.RightToLeft,
-                    Items = items,
-                    Template = GetTemplate()
-                };
+                new ComboBoxItem()
+                { 
+                    Content = new Control()
+                }
+            };
+            var target = new ComboBox
+            {
+                FlowDirection = FlowDirection.RightToLeft,
+                Items = items,
+                Template = GetTemplate()
+            };
 
-                var root = new TestRoot(target);
-                target.ApplyTemplate();
-                target.SelectedIndex = 0;
+            var root = new TestRoot(target);
+            target.ApplyTemplate();
+            target.SelectedIndex = 0;
 
-                var rectangle = target.GetValue(ComboBox.SelectionBoxItemProperty) as Rectangle;
+            var rectangle = target.GetValue(ComboBox.SelectionBoxItemProperty) as Rectangle;
 
-                Assert.Equal(FlowDirection.LeftToRight, rectangle.FlowDirection);
-            }
+            Assert.Equal(FlowDirection.LeftToRight, rectangle.FlowDirection);
         }
 
         [Fact]
-        public void FlowDirection_Of_RectangleContent_Updated_After_Change_ComboBox()
+        public void FlowDirection_Of_RectangleContent_Updated_After_InvalidateMirrorTransform()
         {
-            using (UnitTestApplication.Start(TestServices.RealStyler))
+            var parentContent = new Decorator()
             {
-                var items = new[]
-                {
-                    new ComboBoxItem()
-                    { 
-                        Content = new Control()
-                    }
-                };
-                var target = new ComboBox
+                Child = new Control()
+            };
+            var items = new[]
+            { 
+                new ComboBoxItem()
                 {
-                    FlowDirection = FlowDirection.RightToLeft,
-                    Items = items,
-                    Template = GetTemplate()
-                };
-
-                var root = new TestRoot(target);
-                target.ApplyTemplate();
-                target.Presenter.ApplyTemplate();
-                target.SelectedIndex = 0;
-                ((ContentPresenter)target.Presenter).UpdateChild();
-
-                var rectangle = target.GetValue(ComboBox.SelectionBoxItemProperty) as Rectangle;
-
-                // need help here, the 'rectangle' isn't connected to visual tree for some reason
+                    Content = parentContent.Child
+                }
+            };
+            var target = new ComboBox
+            {
+                FlowDirection = FlowDirection.RightToLeft,
+                Items = items,
+                Template = GetTemplate()
+            };
 
-                Assert.True(rectangle.HasMirrorTransform);
+            var root = new TestRoot(target);
+            target.ApplyTemplate();
+            target.SelectedIndex = 0;
 
-                target.FlowDirection = FlowDirection.LeftToRight;
+            var rectangle = target.GetValue(ComboBox.SelectionBoxItemProperty) as Rectangle;
+            Assert.Equal(FlowDirection.LeftToRight, rectangle.FlowDirection);
 
-                Assert.False(rectangle.HasMirrorTransform);
-            }
+            parentContent.FlowDirection = FlowDirection.RightToLeft;
+            target.InvalidateMirrorTransform();
+            
+            Assert.Equal(FlowDirection.RightToLeft, rectangle.FlowDirection);
         }
 
         [Fact]
-        public void FlowDirection_Of_RectangleContent_Updated_After_Content_In_VisualTree()
+        public void FlowDirection_Of_RectangleContent_Updated_After_OpenPopup()
         {
-            using (UnitTestApplication.Start(TestServices.RealFocus))
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                Control content;
-                var items = new[]
+                var parentContent = new Decorator()
                 {
+                    Child = new Control()
+                };
+                var items = new[]
+                { 
                     new ComboBoxItem()
                     {
-                        Content = content = new Control()
+                        Content = parentContent.Child
                     }
                 };
                 var target = new ComboBox
@@ -425,14 +422,17 @@ namespace Avalonia.Controls.UnitTests
 
                 var root = new TestRoot(target);
                 target.ApplyTemplate();
-                target.Presenter.ApplyTemplate();
                 target.SelectedIndex = 0;
 
-                // need help here how to connect 'content' to visual tree, or how to open popup
-
-
                 var rectangle = target.GetValue(ComboBox.SelectionBoxItemProperty) as Rectangle;
+                Assert.Equal(FlowDirection.LeftToRight, rectangle.FlowDirection);
 
+                parentContent.FlowDirection = FlowDirection.RightToLeft;
+
+                var popup = target.GetVisualDescendants().OfType<Popup>().First();
+                popup.PlacementTarget = new Window();
+                popup.Open();
+                
                 Assert.Equal(FlowDirection.RightToLeft, rectangle.FlowDirection);
             }
         }