Extern template for template parametrized with incompete type

A compilable example:

main.cpp

#include "test.h"

int main(int argc, char* argv[]) {
    auto myPtr = std::unique_ptr<MyClass>(getMyPtr());
}

test.h

#ifndef TEST_H
#define TEST_H

#include <memory>

class MyClass;
extern template class std::unique_ptr<MyClass>;
MyClass* getMyPtr();

#endif

test.cpp

#include "test.h"

class MyClass {};
template class std::unique_ptr<MyClass>;
MyClass* getMyPtr() { return new MyClass; }

g++ 4.9.2 complains

In file included from c:/devel/mingw32/i686-w64-mingw32/include/c++/memory:81:0,
                 from main.cpp:4:
c:/devel/mingw32/i686-w64-mingw32/include/c++/bits/unique_ptr.h: In instantiation of 'void std::default_delete<_Tp>::operator()(_Tp*) const [with _Tp = MyClass]':
c:/devel/mingw32/i686-w64-mingw32/include/c++/bits/unique_ptr.h:236:16:   required from 'std::unique_ptr<_Tp, _Dp>::~unique_ptr() [with _Tp = MyClass; _Dp = std::default_delete<MyClass>]'
main.cpp:64:53:   required from here
c:/devel/mingw32/i686-w64-mingw32/include/c++/bits/unique_ptr.h:74:22: error: invalid application of 'sizeof' to incomplete type 'MyClass'
  static_assert(sizeof(_Tp)>0,
                      ^

even though MyClass should be visible at the point of template instantiation. Why?

Edit: fixed a typo in example.