make fails on Arch Linux

...
make[1]: Entering directory '/home/milk/tmp/harmonySEQ-0.16/src'
g++ -DLOCALEDIR=\"/usr/local/share/locale\" -DHAVE_CONFIG_H -I. -pthread -I/usr/include/gtkmm-2.4 -I/usr/lib/gtkmm-2.4/include -I/usr/include/atkmm-1.6 -I/usr/include/gtk-unix-print-2.0 -I/usr/include/gtk-2.0 -I/usr/include/gdkmm-2.4 -I/usr/lib/gdkmm-2.4/include -I/usr/include/giomm-2.4 -I/usr/lib/giomm-2.4/include -I/usr/include/pangomm-1.4 -I/usr/lib/pangomm-1.4/include -I/usr/include/glibmm-2.4 -I/usr/lib/glibmm-2.4/include -I/usr/include/cairomm-1.0 -I/usr/lib/cairomm-1.0/include -I/usr/include/sigc++-2.0 -I/usr/lib/sigc++-2.0/include -I/usr/include/gtk-2.0 -I/usr/lib/gtk-2.0/include -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/libdrm -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -I/usr/include/pango-1.0 -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/harfbuzz -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/harfbuzz -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -Wall -O3 -O3 -MT harmonySEQ-MidiDriver.o -MD -MP -MF .deps/harmonySEQ-MidiDriver.Tpo -c -o harmonySEQ-MidiDriver.o `test -f 'MidiDriver.cpp' || echo './'`MidiDriver.cpp
MidiDriver.cpp: In member function ‘void MidiDriver::Open()’:
MidiDriver.cpp:121:9: warning: unused variable ‘x’ [-Wunused-variable]
     int x = snd_seq_set_client_pool_output(seq_handle,2000);
         ^
MidiDriver.cpp: In member function ‘void MidiDriver::ScheduleDiodeEvent(DiodeType, seqHandle, int, double, int, int, int)’:
MidiDriver.cpp:216:87: error: no matching function for call to ‘make_pair(int&, DiodeMidiEvent&)’
     diode_events.insert(std::make_pair<int,DiodeMidiEvent>(diode_event_id_next,diodeev));
                                                                                       ^
In file included from /usr/include/c++/6.2.1/bits/stl_algobase.h:64:0,
                 from /usr/include/c++/6.2.1/vector:60,
                 from global.h:28,
                 from MidiDriver.cpp:23:
/usr/include/c++/6.2.1/bits/stl_pair.h:425:5: note: candidate: template<class _T1, class _T2> constexpr std::pair<typename std::__decay_and_strip<_Tp>::__type, typename std::__decay_and_strip<_T2>::__type> std::make_pair(_T1&&, _T2&&)
     make_pair(_T1&& __x, _T2&& __y)
     ^~~~~~~~~
/usr/include/c++/6.2.1/bits/stl_pair.h:425:5: note: template argument deduction/substitution failed:
MidiDriver.cpp:216:60: note: cannot convert ‘((MidiDriver*)this)->MidiDriver::diode_event_id_next’ (type ‘int’) to type ‘int&&’
     diode_events.insert(std::make_pair<int,DiodeMidiEvent>(diode_event_id_next,diodeev));
                                                            ^~~~~~~~~~~~~~~~~~~
make[1]: *** [Makefile:433: harmonySEQ-MidiDriver.o] Error 1
make[1]: Leaving directory '/home/milk/tmp/harmonySEQ-0.16/src'
make: *** [Makefile:263: all] Error 2