diff --git a/src/Models/Preference.cs b/src/Models/Preference.cs
index 9b3e4bff..635ffb9e 100644
--- a/src/Models/Preference.cs
+++ b/src/Models/Preference.cs
@@ -78,7 +78,6 @@ namespace SourceGit.Models {
         ///     外部合并工具配置
         /// </summary>
         public class MergeToolInfo {
-
             /// <summary>
             ///     合并工具类型
             /// </summary>
@@ -87,7 +86,7 @@ namespace SourceGit.Models {
             /// <summary>
             ///     合并工具可执行文件路径
             /// </summary>
-            public string Path { get; set; }
+            public string Path { get; set; } = "";
         }
 
         /// <summary>
diff --git a/src/Views/Preference.xaml.cs b/src/Views/Preference.xaml.cs
index 8587f2fb..dd28ff71 100644
--- a/src/Views/Preference.xaml.cs
+++ b/src/Views/Preference.xaml.cs
@@ -87,17 +87,18 @@ namespace SourceGit.Views {
         }
 
         private void MergeToolChanged(object sender, SelectionChangedEventArgs e) {
-            var selector = sender as ComboBox;
-            var type = (int)selector.SelectedValue;
+            var type = (int)(sender as ComboBox).SelectedValue;
             var tool = Models.MergeTool.Supported.Find(x => x.Type == type);
             if (tool == null) return;
 
-            Models.Preference.Instance.MergeTool.Path = tool.Finder();
             MergeCmd = tool.Cmd;
-
-            txtMergeExec?.GetBindingExpression(TextBox.TextProperty).UpdateTarget();
             txtMergeCmd?.GetBindingExpression(TextBlock.TextProperty).UpdateTarget();
 
+            if (IsLoaded) {
+                Models.Preference.Instance.MergeTool.Path = tool.Finder();
+                txtMergeExec?.GetBindingExpression(TextBox.TextProperty).UpdateTarget();
+            }
+
             e.Handled = true;
         }