Hi, I use gcc-5.1.0 on Windows (x86_64-posix-seh-rev0, Built by MinGW-W64 project). I have the following template class: template <class T> struct StaticObject { static T & getInstance() { static T t; std::cout << "static object " << typeid(T).name() << " at " << &t << " = "<< t <<std::endl; return t; } }; What i want to achieve is to have one instance of say StaticObject<int> through my EXE and several DLLs modules with use of explicit instantiation. So in one of my DLLs (inst.dll) i have explicit instantiation of StaticObject<int> - inst.cpp: #include "static_object.h" template struct StaticObject<int>; And there is #include “externs.h” in each source file that use this static object to prevent it from implicit instantiation - externs.h : #pragma once #include "static_object.h" extern template struct StaticObject<int>; There is calls to StaticObject<int>::getInstance() in EXE and DLL modules and what i get is different behavior with optimisation turned on and off. It works as expected: 1) with optimisation turned off and 2) with following flags: “-Ox -fno-inline”, where ‘x’ is one of optimisation levels 1,2,3. And it doesn’t work with any (1,2,3) level of optimisation turned on, so i get instances of StaticObject<int> in each DLL and EXE. Please see my github project for reference - https://github.com/dlardi/mingw_static_test Is this a gcc's bug?