Hello, When using the boost interval library we get a run-time assertion failure in debug with 64 bit Visual Studio 2005 and up. In file msvc_rounding_control.hpp, the function set_rounding_mode(..) calls _control87(..) which in debug will cause an assert to fail. According to microsoft documentation: "On the x64 architecture, changing the floating-point precision is not supported. If the precision control mask is used on that platform, the invalid parameter handler is invoked, as described in Parameter Validation." Run-time library reference: http://msdn.microsoft.com/en-us/library/e9b52ceh%28VS.80%29.aspx Visual Studio 2010 documentation: http://msdn.microsoft.com/en-us/library/c9676k6h.aspx In release the invalid parameter handler is not invoked so the code runs without complaining, but the rounding-mode is of course not changed. Did anybody else run into this problem? Iman