Hi, I noticed that system/error_code.hpp caused some unexpected increase in compilation time, and looked trough its includes. The following seems not needed: #include <boost/cstdint.hpp> #include <boost/assert.hpp> #include <boost/operators.hpp> #include <boost/noncopyable.hpp> // 1) #include <stdexcept> #include <functional> // 2) 1) noncopyable is used to tell that a class (error_category) with pure virtual functions cannot be copied. This is implicit in the language, so really not needed. Unless there's a compelling reason to make sure derived classes can't be copyable either, but I didn't see any reason for this? I didn't look very close though, could've missed it. 2) inclusion of <functional> seems only needed to have the following: bool operator<( const error_category & rhs ) const { return std::less<const error_category*>()( this, &rhs ); } I can't guess the reason for using std::less instead of simply writing '<', but surely it can be expressed without std::less, no? And before getting the common Booster's answer when asking to remove #includes: Yes, I am aware of precompiled headers. I use them, too. =) Cheers, Christian P.S. Would it be too much to ask for having a separate header for the error_code's ostream operators?