diff --git a/src/win32_window.c b/src/win32_window.c
index f46a44a6e..931417e7e 100644
--- a/src/win32_window.c
+++ b/src/win32_window.c
@@ -566,7 +566,10 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
             else
                 _glfwInputKey(window, key, scancode, action, mods);
 
-            break;
+            if(wParam == VK_MENU) {
+                return 0;
+            }
+            break; // #fix: disable system default ALT process, solve dead block problem when glfw-window is a cross-thread child window.
         }
 
         case WM_LBUTTONDOWN: