QT5: Promoting widget inside a promoted form class

Hello there! I have a MainWindow form. I put a widget inside it and promote it to my class 1. But my class 1 has a form that contains a widget promoted to my class 2. When I try to compile, it gave me the following error: form1.obj:-1: error: LNK2001: unresolved external symbol "public: __thiscall Form2::Form2(class QWidget *)" (??0Form2@@QAE@PAVQWidget@@@Z) What could I do to accomplise this? Is this impossible? Thanks you for your answers and time.