diff --git a/include/winnls.h b/include/winnls.h
index 96f60de1268..d6fcf6e4535 100644
--- a/include/winnls.h
+++ b/include/winnls.h
@@ -921,6 +921,7 @@ WINBASEAPI LANGID      WINAPI GetSystemDefaultUILanguage(void);
 WINBASEAPI BOOL        WINAPI GetSystemPreferredUILanguages(DWORD,ULONG*,WCHAR*,ULONG*);
 WINBASEAPI LCID        WINAPI GetThreadLocale(void);
 WINBASEAPI BOOL        WINAPI GetThreadPreferredUILanguages(DWORD,ULONG*,WCHAR*,ULONG*);
+WINBASEAPI LANGID      WINAPI GetThreadUILanguage(void);
 WINBASEAPI INT         WINAPI GetTimeFormatA(LCID,DWORD,const SYSTEMTIME*,LPCSTR,LPSTR,INT);
 WINBASEAPI INT         WINAPI GetTimeFormatEx(LPCWSTR,DWORD,const SYSTEMTIME*,LPCWSTR,LPWSTR,INT);
 WINBASEAPI INT         WINAPI GetTimeFormatW(LCID,DWORD,const SYSTEMTIME*,LPCWSTR,LPWSTR,INT);