diff --git a/win32ss/user/ntuser/defwnd.c b/win32ss/user/ntuser/defwnd.c
index dba5c7b567b..77b8235b005 100644
--- a/win32ss/user/ntuser/defwnd.c
+++ b/win32ss/user/ntuser/defwnd.c
@@ -580,6 +580,57 @@ DefWndScreenshot(PWND pWnd)
     UserCloseClipboard();
 }
 
+// WM_POPUPSYSTEMMENU
+static BOOL
+co_UserTrackSystemMenu(_In_ PWND pWnd, _In_ LONG nClickPos, _In_opt_ PUINT puCmdType)
+{
+    USER_REFERENCE_ENTRY MenuRef, WndRef;
+    PMENU pMenu;
+    UINT uDefaultCmd;
+
+    FIXME("co_UserTrackSystemMenu() called\n"); // Useful trace, while working on CORE-3247
+
+    UserRefObjectCo(pWnd, &WndRef);
+
+    // Check style and make window foreground
+    if ((pWnd->style & WS_DISABLED) ||
+        (pWnd->state2 & WNDS2_INDESTROY) ||
+        (pWnd->head.pti->MessageQueue != gpqForeground && !co_IntSetForegroundWindow(pWnd)))
+    {
+        UserDerefObjectCo(pWnd);
+        return FALSE;
+    }
+
+    // Get the window's system menu
+    pMenu = IntGetSystemMenu(pWnd, FALSE);
+    if (!pMenu)
+    {
+        UserDerefObjectCo(pWnd);
+        return FALSE;
+    }
+    UserRefObjectCo(pMenu, &MenuRef);
+
+    // Set default menu item
+    if (puCmdType)
+        uDefaultCmd = *puCmdType;
+    else if (pWnd->style & (WS_MINIMIZE | WS_MAXIMIZE))
+        uDefaultCmd = SC_RESTORE;
+    else
+        uDefaultCmd = SC_MAXIMIZE;
+    UserSetMenuDefaultItem(pMenu, uDefaultCmd, FALSE);
+
+    if (nClickPos == -1) // Input from keyboard?
+        FIXME("Use WM_KLUDGEMINRECT and TPM_VERTICAL\n");
+
+    // Show the menu and wait for menu tracking ending
+    IntTrackPopupMenuEx(pMenu, TPM_LEFTBUTTON | TPM_RIGHTBUTTON | TPM_SYSTEM_MENU,
+                        LOWORD(nClickPos), HIWORD(nClickPos), pWnd, NULL);
+
+    UserDerefObjectCo(pMenu);
+    UserDerefObjectCo(pWnd);
+    return TRUE;
+}
+
 /*
    Win32k counterpart of User DefWindowProc
  */
@@ -697,6 +748,12 @@ IntDefWindowProc(
          UserDerefObjectCo(Wnd->spwndParent);
          break;
 
+      case WM_POPUPSYSTEMMENU:
+         /* This is an undocumented message used by the windows taskbar to
+            display the system menu of windows that belong to other processes. */
+         co_UserTrackSystemMenu(Wnd, (LONG)lParam, NULL);
+         break;
+
       case WM_KEYF1:
       {
          HELPINFO hi;
diff --git a/win32ss/user/user32/windows/defwnd.c b/win32ss/user/user32/windows/defwnd.c
index 70dad210604..f7a68fd84bb 100644
--- a/win32ss/user/user32/windows/defwnd.c
+++ b/win32ss/user/user32/windows/defwnd.c
@@ -327,21 +327,6 @@ User32DefWindowProc(HWND hWnd,
         case WM_DEVICECHANGE:
             return TRUE;
 
-        case WM_POPUPSYSTEMMENU:
-        {
-            /* This is an undocumented message used by the windows taskbar to
-               display the system menu of windows that belong to other processes. */
-            HMENU menu = GetSystemMenu(hWnd, FALSE);
-            ERR("WM_POPUPSYSTEMMENU\n");
-            if (menu)
-            {
-                SetForegroundWindow(hWnd);
-                TrackPopupMenu(menu, TPM_LEFTBUTTON|TPM_RIGHTBUTTON|TPM_SYSTEM_MENU,
-                               LOWORD(lParam), HIWORD(lParam), 0, hWnd, NULL);
-            }
-            return 0;
-        }
-
         case WM_RBUTTONUP:
         {
             POINT Pt;
@@ -798,6 +783,7 @@ User32DefWindowProc(HWND hWnd,
         case WM_WINDOWPOSCHANGED:
         case WM_APPCOMMAND:
         case WM_SETCURSOR:
+        case WM_POPUPSYSTEMMENU:
 GoSS:
         {
             LRESULT lResult;