diff --git a/dlls/user32/tests/msg.c b/dlls/user32/tests/msg.c
index 5f10a89ec29..b014dd9a0f7 100644
--- a/dlls/user32/tests/msg.c
+++ b/dlls/user32/tests/msg.c
@@ -14598,6 +14598,153 @@ static void test_TrackPopupMenuEmpty(void)
     DestroyWindow(hwnd);
 }
 
+static const struct message send_message_1[] = {
+    { WM_USER+2, sent|wparam|lparam, 0, 0 },
+    { WM_USER, sent|wparam|lparam, 0, 0 },
+    { 0 }
+};
+static const struct message send_message_2[] = {
+    { WM_USER+4, sent|wparam|lparam, 0, 0 },
+    { 0 }
+};
+static const struct message send_message_3[] = {
+    { WM_USER+3, sent|wparam|lparam, 0, 0 },
+    { WM_USER+1, sent|wparam|lparam, 0, 0 },
+    { 0 }
+};
+
+static DWORD WINAPI SendMessage_thread_1(void *param)
+{
+    struct wnd_event *wnd_event = param;
+
+    trace("thread: starting\n");
+    WaitForSingleObject(wnd_event->start_event, INFINITE);
+
+    trace("thread: call PostMessage\n");
+    PostMessageA(wnd_event->hwnd, WM_USER, 0, 0);
+
+    trace("thread: call PostMessage\n");
+    PostMessageA(wnd_event->hwnd, WM_USER+1, 0, 0);
+
+    trace("thread: call SendMessage\n");
+    SendMessageA(wnd_event->hwnd, WM_USER+2, 0, 0);
+
+    trace("thread: call SendMessage\n");
+    SendMessageA(wnd_event->hwnd, WM_USER+3, 0, 0);
+
+    return 0;
+}
+
+static DWORD WINAPI SendMessage_thread_2(void *param)
+{
+    struct wnd_event *wnd_event = param;
+
+    trace("thread: starting\n");
+    WaitForSingleObject(wnd_event->start_event, INFINITE);
+
+    trace("thread: call PostMessage\n");
+    PostMessageA(wnd_event->hwnd, WM_USER, 0, 0);
+
+    trace("thread: call PostMessage\n");
+    PostMessageA(wnd_event->hwnd, WM_USER+1, 0, 0);
+
+    /* this leads to sending an internal message under Wine */
+    trace("thread: call EnableWindow\n");
+    EnableWindow(wnd_event->hwnd, TRUE);
+
+    trace("thread: call SendMessage\n");
+    SendMessageA(wnd_event->hwnd, WM_USER+2, 0, 0);
+
+    trace("thread: call SendMessage\n");
+    SendMessageA(wnd_event->hwnd, WM_USER+3, 0, 0);
+
+    return 0;
+}
+
+static void test_SendMessage_other_thread(int thread_n)
+{
+    DWORD qs_all_input = QS_ALLINPUT & ~QS_RAWINPUT;
+    HANDLE hthread;
+    struct wnd_event wnd_event;
+    DWORD tid, ret;
+    MSG msg;
+
+    wnd_event.start_event = CreateEventA(NULL, 0, 0, NULL);
+
+    wnd_event.hwnd = CreateWindowExA(0, "TestWindowClass", NULL, WS_OVERLAPPEDWINDOW,
+                                     100, 100, 200, 200, 0, 0, 0, NULL);
+    ok(wnd_event.hwnd != 0, "CreateWindowEx failed\n");
+
+    hthread = CreateThread(NULL, 0, thread_n == 1 ? SendMessage_thread_1 : SendMessage_thread_2, &wnd_event, 0, &tid);
+    ok(hthread != NULL, "CreateThread failed, error %d\n", GetLastError());
+    CloseHandle(hthread);
+
+    flush_events();
+    flush_sequence();
+
+    ret = GetQueueStatus(QS_SENDMESSAGE);
+    ok(ret == 0, "wrong status %08x\n", ret);
+
+    SetEvent(wnd_event.start_event);
+
+    /* wait for other thread's SendMessage */
+    for (;;)
+    {
+        ret = GetQueueStatus(QS_SENDMESSAGE);
+        if (ret == MAKELONG(QS_SENDMESSAGE, QS_SENDMESSAGE)) break;
+        Sleep(50);
+    }
+
+    ret = GetQueueStatus(QS_SENDMESSAGE|QS_POSTMESSAGE);
+todo_wine
+    ok(ret == MAKELONG(QS_POSTMESSAGE, QS_SENDMESSAGE|QS_POSTMESSAGE), "wrong status %08x\n", ret);
+
+    trace("main: call GetMessage\n");
+    GetMessageA(&msg, 0, 0, 0);
+    ok(msg.message == WM_USER, "expected WM_USER, got %04x\n", msg.message);
+    DispatchMessageA(&msg);
+    ok_sequence(send_message_1, "SendMessage from other thread 1", thread_n == 2);
+
+    /* intentionally yield */
+    MsgWaitForMultipleObjects(0, NULL, FALSE, 100, qs_all_input);
+
+    trace("main: call SendMessage\n");
+    SendMessageA(wnd_event.hwnd, WM_USER+4, 0, 0);
+    ok_sequence(send_message_2, "SendMessage from other thread 2", FALSE);
+
+    ret = GetQueueStatus(QS_SENDMESSAGE|QS_POSTMESSAGE);
+    ok(ret == MAKELONG(QS_SENDMESSAGE, QS_SENDMESSAGE|QS_POSTMESSAGE), "wrong status %08x\n", ret);
+
+    trace("main: call PeekMessage\n");
+    ok(PeekMessageA(&msg, 0, 0, 0, PM_REMOVE), "PeekMessage should not fail\n");
+    ok(msg.message == WM_USER+1, "expected WM_USER+1, got %04x\n", msg.message);
+    DispatchMessageA(&msg);
+    ok_sequence(send_message_3, "SendMessage from other thread 3", thread_n == 2);
+
+    /* intentionally yield */
+    MsgWaitForMultipleObjects(0, NULL, FALSE, 100, qs_all_input);
+
+    ret = GetQueueStatus(QS_SENDMESSAGE|QS_POSTMESSAGE);
+    /* FIXME: remove once Wine is fixed */
+if (thread_n == 2) todo_wine
+    ok(ret == 0, "wrong status %08x\n", ret);
+else
+    ok(ret == 0, "wrong status %08x\n", ret);
+
+    trace("main: call PeekMessage\n");
+    ok(!PeekMessageA(&msg, 0, 0, 0, PM_REMOVE), "PeekMessage should fail\n");
+    ok_sequence(WmEmptySeq, "SendMessage from other thread 4", thread_n == 2);
+
+    ret = GetQueueStatus(QS_SENDMESSAGE|QS_POSTMESSAGE);
+    ok(ret == 0, "wrong status %08x\n", ret);
+
+    trace("main: call DestroyWindow\n");
+    DestroyWindow(msg.hwnd);
+
+    flush_events();
+    flush_sequence();
+}
+
 static void init_funcs(void)
 {
     HMODULE hKernel32 = GetModuleHandleA("kernel32.dll");
@@ -14675,6 +14822,9 @@ START_TEST(msg)
         pUnhookWinEvent = 0;
     }
     hEvent_hook = 0;
+
+    test_SendMessage_other_thread(1);
+    test_SendMessage_other_thread(2);
     test_SetFocus();
     test_SetParent();
     test_PostMessage();