diff --git a/BizHawk.Client.EmuHawk/tools/Lua/LuaWinform.cs b/BizHawk.Client.EmuHawk/tools/Lua/LuaWinform.cs
index 9034da897a..b62948d111 100644
--- a/BizHawk.Client.EmuHawk/tools/Lua/LuaWinform.cs
+++ b/BizHawk.Client.EmuHawk/tools/Lua/LuaWinform.cs
@@ -30,7 +30,8 @@ namespace BizHawk.Client.EmuHawk
 
 		public void DoLuaEvent(IntPtr handle)
 		{
-			LuaSandbox.Sandbox(_ownerFile.Thread, () =>
+			// #1957 - ownerFile can be full, if the script that generated the form ended which will happen if the script does not have a while true loop
+			LuaSandbox.Sandbox(_ownerFile?.Thread, () =>
 			{
 				Environment.CurrentDirectory = _currentDirectory;
 				foreach (LuaEvent luaEvent in ControlEvents)