diff --git a/dlls/user32/message.c b/dlls/user32/message.c
index 2255e0ee4ba..dff7ca24786 100644
--- a/dlls/user32/message.c
+++ b/dlls/user32/message.c
@@ -1807,7 +1807,7 @@ BOOL WINAPI PostMessageW( HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam )
         return TRUE;
     }
 
-    if (!hwnd) return PostThreadMessageW( GetCurrentThreadId(), msg, wparam, lparam );
+    if (!hwnd) return NtUserPostThreadMessage( GetCurrentThreadId(), msg, wparam, lparam );
 
     if (!(info.dest_tid = GetWindowThreadProcessId( hwnd, NULL ))) return FALSE;
 
@@ -1823,32 +1823,7 @@ BOOL WINAPI PostMessageW( HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam )
 BOOL WINAPI PostThreadMessageA( DWORD thread, UINT msg, WPARAM wparam, LPARAM lparam )
 {
     if (!map_wparam_AtoW( msg, &wparam, WMCHAR_MAP_POSTMESSAGE )) return TRUE;
-    return PostThreadMessageW( thread, msg, wparam, lparam );
-}
-
-
-/**********************************************************************
- *		PostThreadMessageW  (USER32.@)
- */
-BOOL WINAPI PostThreadMessageW( DWORD thread, UINT msg, WPARAM wparam, LPARAM lparam )
-{
-    struct send_message_info info;
-
-    if (is_pointer_message( msg, wparam ))
-    {
-        SetLastError( ERROR_MESSAGE_SYNC_ONLY );
-        return FALSE;
-    }
-    if (USER_IsExitingThread( thread )) return TRUE;
-
-    info.type     = MSG_POSTED;
-    info.dest_tid = thread;
-    info.hwnd     = 0;
-    info.msg      = msg;
-    info.wparam   = wparam;
-    info.lparam   = lparam;
-    info.flags    = 0;
-    return put_message_in_queue( &info, NULL );
+    return NtUserPostThreadMessage( thread, msg, wparam, lparam );
 }
 
 
diff --git a/dlls/user32/user32.spec b/dlls/user32/user32.spec
index 89c9d76f568..2c4dba5cd86 100644
--- a/dlls/user32/user32.spec
+++ b/dlls/user32/user32.spec
@@ -571,7 +571,7 @@
 @ stdcall PostMessageW(long long long long)
 @ stdcall PostQuitMessage(long)
 @ stdcall PostThreadMessageA(long long long long)
-@ stdcall PostThreadMessageW(long long long long)
+@ stdcall PostThreadMessageW(long long long long) NtUserPostThreadMessage
 @ stdcall PrintWindow(long long long)
 @ stdcall PrivateExtractIconExA(str long ptr ptr long)
 @ stdcall PrivateExtractIconExW(wstr long ptr ptr long)
diff --git a/dlls/win32u/gdiobj.c b/dlls/win32u/gdiobj.c
index 4d78c99bbc7..645e29305e8 100644
--- a/dlls/win32u/gdiobj.c
+++ b/dlls/win32u/gdiobj.c
@@ -1193,6 +1193,7 @@ static struct unix_funcs unix_funcs =
     NtUserMoveWindow,
     NtUserMsgWaitForMultipleObjectsEx,
     NtUserPeekMessage,
+    NtUserPostThreadMessage,
     NtUserRedrawWindow,
     NtUserRegisterClassExWOW,
     NtUserRegisterHotKey,
diff --git a/dlls/win32u/message.c b/dlls/win32u/message.c
index 73312424283..f3e695ea16a 100644
--- a/dlls/win32u/message.c
+++ b/dlls/win32u/message.c
@@ -2407,6 +2407,30 @@ BOOL WINAPI NtUserPostMessage( HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam
     return user_callbacks->pPostMessageW( hwnd, msg, wparam, lparam );
 }
 
+/**********************************************************************
+ *           NtUserPostThreadMessage  (win32u.@)
+ */
+BOOL WINAPI NtUserPostThreadMessage( DWORD thread, UINT msg, WPARAM wparam, LPARAM lparam )
+{
+    struct send_message_info info;
+
+    if (is_pointer_message( msg, wparam ))
+    {
+        SetLastError( ERROR_MESSAGE_SYNC_ONLY );
+        return FALSE;
+    }
+    if (is_exiting_thread( thread )) return TRUE;
+
+    info.type     = MSG_POSTED;
+    info.dest_tid = thread;
+    info.hwnd     = 0;
+    info.msg      = msg;
+    info.wparam   = wparam;
+    info.lparam   = lparam;
+    info.flags    = 0;
+    return put_message_in_queue( &info, NULL );
+}
+
 LRESULT WINAPI NtUserMessageCall( HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam,
                                   void *result_info, DWORD type, BOOL ansi )
 {
diff --git a/dlls/win32u/win32u.spec b/dlls/win32u/win32u.spec
index 31561cb3a1c..7670e1a5310 100644
--- a/dlls/win32u/win32u.spec
+++ b/dlls/win32u/win32u.spec
@@ -1104,7 +1104,7 @@
 @ stub NtUserPhysicalToLogicalPoint
 @ stub NtUserPostKeyboardInputMessage
 @ stub NtUserPostMessage
-@ stub NtUserPostThreadMessage
+@ stdcall NtUserPostThreadMessage(long long long long)
 @ stub NtUserPrintWindow
 @ stub NtUserProcessConnect
 @ stub NtUserProcessInkFeedbackCommand
diff --git a/dlls/win32u/win32u_private.h b/dlls/win32u/win32u_private.h
index c844603640e..ffd050adbcf 100644
--- a/dlls/win32u/win32u_private.h
+++ b/dlls/win32u/win32u_private.h
@@ -242,6 +242,7 @@ struct unix_funcs
     DWORD    (WINAPI *pNtUserMsgWaitForMultipleObjectsEx)( DWORD count, const HANDLE *handles,
                                                            DWORD timeout, DWORD mask, DWORD flags );
     BOOL     (WINAPI *pNtUserPeekMessage)( MSG *msg_out, HWND hwnd, UINT first, UINT last, UINT flags );
+    BOOL     (WINAPI *pNtUserPostThreadMessage)( DWORD thread, UINT msg, WPARAM wparam, LPARAM lparam );
     BOOL     (WINAPI *pNtUserRedrawWindow)( HWND hwnd, const RECT *rect, HRGN hrgn, UINT flags );
     ATOM     (WINAPI *pNtUserRegisterClassExWOW)( const WNDCLASSEXW *wc, UNICODE_STRING *name,
                                                   UNICODE_STRING *version,
diff --git a/dlls/win32u/wrappers.c b/dlls/win32u/wrappers.c
index 4f7c6191df8..159cade9aea 100644
--- a/dlls/win32u/wrappers.c
+++ b/dlls/win32u/wrappers.c
@@ -977,6 +977,12 @@ BOOL WINAPI NtUserPeekMessage( MSG *msg_out, HWND hwnd, UINT first, UINT last, U
     return unix_funcs->pNtUserPeekMessage( msg_out, hwnd, first, last, flags );
 }
 
+BOOL WINAPI NtUserPostThreadMessage( DWORD thread, UINT msg, WPARAM wparam, LPARAM lparam )
+{
+    if (!unix_funcs) return FALSE;
+    return unix_funcs->pNtUserPostThreadMessage( thread, msg, wparam, lparam );
+}
+
 BOOL WINAPI NtUserRedrawWindow( HWND hwnd, const RECT *rect, HRGN hrgn, UINT flags )
 {
     if (!unix_funcs) return FALSE;