Using Arduino IDE 1.6.13 Hourly Build 2016/10/03 06:51 with Windows 7 64 bit https://github.com/arduino/Arduino/pull/3186 added support for including .hpp and .hh files from libraries. If I have a library installed with the folder structure: foo |_foo.h |_foo.hh |_foo.hpp With Arduino IDE 1.6.6 or newer, doing: ``` arduino #include <foo.hh> ``` or ``` arduino #include <foo.hpp> ``` causes compilation to fail: ``` fatal error: bar.hh: No such file or directory #include <foo.hh> ``` It will only compile if I do: ``` arduino #include <foo.h> #include <foo.hh> ``` Using Arduino IDE 1.6.5-r5 I don't need to include the .h file.