diff --git a/reactos/include/psdk/msacm.h b/reactos/include/psdk/msacm.h
index 8a2c8e7d62a..c4da171719f 100644
--- a/reactos/include/psdk/msacm.h
+++ b/reactos/include/psdk/msacm.h
@@ -25,6 +25,8 @@
 extern "C" {
 #endif /* defined(__cplusplus) */
 
+#include <pshpack1.h>
+
 #define ACMAPI              WINAPI
 
 /***********************************************************************
@@ -773,6 +775,8 @@ MMRESULT WINAPI acmStreamUnprepareHeader(
   HACMSTREAM has, PACMSTREAMHEADER pash, DWORD fdwUnprepare
 );
 
+#include <poppack.h>
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif /* defined(__cplusplus) */