diff --git a/dlls/kernel32/string.c b/dlls/kernel32/string.c
index ecac281f133..1f606fd7f6c 100644
--- a/dlls/kernel32/string.c
+++ b/dlls/kernel32/string.c
@@ -36,7 +36,7 @@
 
 
 static INT (WINAPI *pLoadStringA)(HINSTANCE, UINT, LPSTR, INT);
-static INT (WINAPI *pwvsprintfA)(LPSTR, LPCSTR, va_list);
+static INT (WINAPI *pwvsprintfA)(LPSTR, LPCSTR, __ms_va_list);
 
 
 /***********************************************************************
@@ -118,7 +118,7 @@ INT WINAPI k32LoadStringA(HINSTANCE instance, UINT resource_id,
 /***********************************************************************
  *		k32wvsprintfA   (KERNEL32.16)
  */
-INT WINAPI k32wvsprintfA(LPSTR buffer, LPCSTR spec, va_list args)
+INT WINAPI k32wvsprintfA(LPSTR buffer, LPCSTR spec, __ms_va_list args)
 {
     if(!pwvsprintfA) pwvsprintfA = user32_proc_address("wvsprintfA");
     return (*pwvsprintfA)(buffer, spec, args);
@@ -130,12 +130,12 @@ INT WINAPI k32wvsprintfA(LPSTR buffer, LPCSTR spec, va_list args)
  */
 INT WINAPIV k32wsprintfA(LPSTR buffer, LPCSTR spec, ...)
 {
-    va_list args;
+    __ms_va_list args;
     INT res;
 
-    va_start(args, spec);
+    __ms_va_start(args, spec);
     res = k32wvsprintfA(buffer, spec, args);
-    va_end(args);
+    __ms_va_end(args);
     return res;
 }
 
diff --git a/dlls/user32/wsprintf.c b/dlls/user32/wsprintf.c
index 7f98bee01a6..6cb4912f901 100644
--- a/dlls/user32/wsprintf.c
+++ b/dlls/user32/wsprintf.c
@@ -385,7 +385,7 @@ static INT16 wvsnprintf16( LPSTR buffer, UINT16 maxlen, LPCSTR spec, VA_LIST16 a
 /***********************************************************************
  *           wvsnprintfA   (internal)
  */
-static INT wvsnprintfA( LPSTR buffer, UINT maxlen, LPCSTR spec, va_list args )
+static INT wvsnprintfA( LPSTR buffer, UINT maxlen, LPCSTR spec, __ms_va_list args )
 {
     WPRINTF_FORMAT format;
     LPSTR p = buffer;
@@ -488,7 +488,7 @@ static INT wvsnprintfA( LPSTR buffer, UINT maxlen, LPCSTR spec, va_list args )
 /***********************************************************************
  *           wvsnprintfW   (internal)
  */
-static INT wvsnprintfW( LPWSTR buffer, UINT maxlen, LPCWSTR spec, va_list args )
+static INT wvsnprintfW( LPWSTR buffer, UINT maxlen, LPCWSTR spec, __ms_va_list args )
 {
     WPRINTF_FORMAT format;
     LPWSTR p = buffer;
@@ -603,7 +603,7 @@ INT16 WINAPI wvsprintf16( LPSTR buffer, LPCSTR spec, VA_LIST16 args )
 /***********************************************************************
  *           wvsprintfA   (USER32.@)
  */
-INT WINAPI wvsprintfA( LPSTR buffer, LPCSTR spec, va_list args )
+INT WINAPI wvsprintfA( LPSTR buffer, LPCSTR spec, __ms_va_list args )
 {
     INT res = wvsnprintfA( buffer, 1024, spec, args );
     return ( res == -1 ) ? 1024 : res;
@@ -613,7 +613,7 @@ INT WINAPI wvsprintfA( LPSTR buffer, LPCSTR spec, va_list args )
 /***********************************************************************
  *           wvsprintfW   (USER32.@)
  */
-INT WINAPI wvsprintfW( LPWSTR buffer, LPCWSTR spec, va_list args )
+INT WINAPI wvsprintfW( LPWSTR buffer, LPCWSTR spec, __ms_va_list args )
 {
     INT res = wvsnprintfW( buffer, 1024, spec, args );
     return ( res == -1 ) ? 1024 : res;
@@ -637,12 +637,12 @@ INT16 WINAPIV wsprintf16( LPSTR buffer, LPCSTR spec, VA_LIST16 valist )
  */
 INT WINAPIV wsprintfA( LPSTR buffer, LPCSTR spec, ... )
 {
-    va_list valist;
+    __ms_va_list valist;
     INT res;
 
-    va_start( valist, spec );
+    __ms_va_start( valist, spec );
     res = wvsnprintfA( buffer, 1024, spec, valist );
-    va_end( valist );
+    __ms_va_end( valist );
     return ( res == -1 ) ? 1024 : res;
 }
 
@@ -652,11 +652,11 @@ INT WINAPIV wsprintfA( LPSTR buffer, LPCSTR spec, ... )
  */
 INT WINAPIV wsprintfW( LPWSTR buffer, LPCWSTR spec, ... )
 {
-    va_list valist;
+    __ms_va_list valist;
     INT res;
 
-    va_start( valist, spec );
+    __ms_va_start( valist, spec );
     res = wvsnprintfW( buffer, 1024, spec, valist );
-    va_end( valist );
+    __ms_va_end( valist );
     return ( res == -1 ) ? 1024 : res;
 }
diff --git a/include/windef.h b/include/windef.h
index 3c9de7a9137..825255b537b 100644
--- a/include/windef.h
+++ b/include/windef.h
@@ -84,6 +84,18 @@ extern "C" {
 # endif
 #endif /* __cdecl */
 
+#ifndef __ms_va_list
+# if defined(__x86_64__) && defined (__GNUC__)
+#  define __ms_va_list __builtin_ms_va_list
+#  define __ms_va_start(list,arg) __builtin_ms_va_start(list,arg)
+#  define __ms_va_end(list) __builtin_ms_va_end(list)
+# else
+#  define __ms_va_list va_list
+#  define __ms_va_start(list,arg) va_start(list,arg)
+#  define __ms_va_end(list) va_end(list)
+# endif
+#endif
+
 #ifdef __WINESRC__
 #define __ONLY_IN_WINELIB(x)	do_not_use_this_in_wine
 #else
diff --git a/include/winuser.h b/include/winuser.h
index 8382a07f22f..fd91d9292c0 100644
--- a/include/winuser.h
+++ b/include/winuser.h
@@ -5068,8 +5068,8 @@ WINUSERAPI VOID        WINAPI mouse_event(DWORD,DWORD,DWORD,DWORD,ULONG_PTR);
 WINUSERAPI INT        WINAPIV wsprintfA(LPSTR,LPCSTR,...);
 WINUSERAPI INT        WINAPIV wsprintfW(LPWSTR,LPCWSTR,...);
 #define                       wsprintf WINELIB_NAME_AW(wsprintf)
-WINUSERAPI INT         WINAPI wvsprintfA(LPSTR,LPCSTR,va_list);
-WINUSERAPI INT         WINAPI wvsprintfW(LPWSTR,LPCWSTR,va_list);
+WINUSERAPI INT         WINAPI wvsprintfA(LPSTR,LPCSTR,__ms_va_list);
+WINUSERAPI INT         WINAPI wvsprintfW(LPWSTR,LPCWSTR,__ms_va_list);
 #define                       wvsprintf WINELIB_NAME_AW(wvsprintf)
 
 /* Undocumented functions */