diff --git a/src/Beutl.Controls/PropertyEditors/Vector2Editor.cs b/src/Beutl.Controls/PropertyEditors/Vector2Editor.cs
index 6564170f0..0ea6a06d0 100644
--- a/src/Beutl.Controls/PropertyEditors/Vector2Editor.cs
+++ b/src/Beutl.Controls/PropertyEditors/Vector2Editor.cs
@@ -121,7 +121,7 @@ void SubscribeEvents2(TextBlock textBlock)
 
     private void OnTextBlockPointerMoved(object sender, PointerEventArgs e)
     {
-        if (!(InnerFirstTextBox.IsKeyboardFocusWithin || InnerSecondTextBox.IsKeyboardFocusWithin)
+        if (!(InnerFirstTextBox.IsKeyboardFocusWithin || InnerSecondTextBox?.IsKeyboardFocusWithin == true)
             && _headerPressed
             && sender is TextBlock headerText)
         {
diff --git a/src/Beutl.Controls/PropertyEditors/Vector3Editor.cs b/src/Beutl.Controls/PropertyEditors/Vector3Editor.cs
index 1ec9df9ab..acd2fcad5 100644
--- a/src/Beutl.Controls/PropertyEditors/Vector3Editor.cs
+++ b/src/Beutl.Controls/PropertyEditors/Vector3Editor.cs
@@ -147,8 +147,8 @@ void SubscribeEvents2(TextBlock textBlock)
     private void OnTextBlockPointerMoved(object sender, PointerEventArgs e)
     {
         if (!(InnerFirstTextBox.IsKeyboardFocusWithin
-            || InnerSecondTextBox.IsKeyboardFocusWithin
-            || InnerThirdTextBox.IsKeyboardFocusWithin)
+            || InnerSecondTextBox?.IsKeyboardFocusWithin == true
+            || InnerThirdTextBox?.IsKeyboardFocusWithin == true)
             && _headerPressed
             && sender is TextBlock headerText)
         {
diff --git a/src/Beutl.Controls/PropertyEditors/Vector4Editor.cs b/src/Beutl.Controls/PropertyEditors/Vector4Editor.cs
index 34c0baebe..b30a703cd 100644
--- a/src/Beutl.Controls/PropertyEditors/Vector4Editor.cs
+++ b/src/Beutl.Controls/PropertyEditors/Vector4Editor.cs
@@ -172,9 +172,9 @@ void SubscribeEvents(TextBox textBox)
     private void OnTextBlockPointerMoved(object sender, PointerEventArgs e)
     {
         if (!(InnerFirstTextBox.IsKeyboardFocusWithin
-            || InnerSecondTextBox.IsKeyboardFocusWithin
-            || InnerThirdTextBox.IsKeyboardFocusWithin
-            || InnerFourthTextBox.IsKeyboardFocusWithin)
+            || InnerSecondTextBox?.IsKeyboardFocusWithin == true
+            || InnerThirdTextBox?.IsKeyboardFocusWithin == true
+            || InnerFourthTextBox?.IsKeyboardFocusWithin == true)
             && _headerPressed)
         {
             Point point = e.GetPosition(_headerText);