diff --git a/dlls/winsock/async.c b/dlls/winsock/async.c
index d78fdf6d659..062bacc3243 100644
--- a/dlls/winsock/async.c
+++ b/dlls/winsock/async.c
@@ -82,9 +82,11 @@
 #include "wingdi.h"
 #include "winuser.h"
 #include "winsock2.h"
+#include "ws2spi.h"
 #include "wine/winsock16.h"
 #include "winnt.h"
 #include "wine/port.h"
+
 #include "debugtools.h"
 
 DEFAULT_DEBUG_CHANNEL(winsock);
@@ -694,7 +696,7 @@ INT16 WINAPI WSACancelAsyncRequest16(HANDLE16 hAsyncTaskHandle)
 /***********************************************************************
  *       WSApSetPostRoutine	(WS2_32.24)
  */
-INT WINAPI WSApSetPostRoutine(LPVOID /* LPWPUPOSTMESSAGE */lpPostRoutine)
+INT WINAPI WSApSetPostRoutine(LPWPUPOSTMESSAGE lpPostRoutine)
 {
     FIXME("(%p), stub !\n", lpPostRoutine);
     return 0;
diff --git a/include/Makefile.in b/include/Makefile.in
index 78eb8b43fca..e671fab5a37 100644
--- a/include/Makefile.in
+++ b/include/Makefile.in
@@ -185,6 +185,7 @@ INSTALLED_INCLUDES = \
 	winver.h \
 	wnaspi32.h \
 	wownt32.h \
+	ws2spi.h \
 	wshisotp.h \
 	wsipx.h \
 	wtypes.h \
diff --git a/include/ws2spi.h b/include/ws2spi.h
new file mode 100644
index 00000000000..7178cf67063
--- /dev/null
+++ b/include/ws2spi.h
@@ -0,0 +1,24 @@
+/* WS2SPI.H -- definitions to be used with the WinSock service provider. */
+
+#ifndef _WINSOCK2SPI_
+#define _WINSOCK2SPI_
+
+#ifndef _WINSOCK2API_
+#include "winsock2.h"
+#endif /* !defined(_WINSOCK2API_) */
+
+#include "pshpack4.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* defined(__cplusplus) */
+
+typedef BOOL WINAPI (*LPWPUPOSTMESSAGE)(HWND,UINT,WPARAM,LPARAM);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif /* defined(__cplusplus) */
+
+#include "poppack.h"
+
+#endif /* !defined(_WINSOCK2SPI_) */