diff --git a/Src/xWorks/GeneratedHtmlViewer.cs b/Src/xWorks/GeneratedHtmlViewer.cs
index a549bf6283..f12e89a46e 100644
--- a/Src/xWorks/GeneratedHtmlViewer.cs
+++ b/Src/xWorks/GeneratedHtmlViewer.cs
@@ -1083,6 +1083,11 @@ private void AddMatchCaseCheckBox()
 			}
 			private void matchCase_CheckedChanged(object sender, EventArgs e)
 			{
+				if (geckoBrowser?.Window == null)
+				{
+					Close();
+					return;
+				}
 				InvokeSearch(SearchText, matchCase.Checked);
 				using (var executor = new AutoJSContext(geckoBrowser.Window))
 				{