diff --git a/AppleWin/source/Structs.h b/AppleWin/source/Structs.h
index e340a22b..410ac976 100644
--- a/AppleWin/source/Structs.h
+++ b/AppleWin/source/Structs.h
@@ -1,3 +1,5 @@
+#pragma once
+
 // Structs used by save-state file
 
 // *** DON'T CHANGE ANY STRUCT WITHOUT CONSIDERING BACKWARDS COMPATIBILITY WITH .AWS FORMAT ***