SystemTimer Installation error

root@ubuntu:~/Development/Teambox# gem install SystemTimer
Building native extensions.  This could take a while...
ERROR:  Error installing SystemTimer:
	ERROR: Failed to build gem native extension.

/usr/local/bin/ruby extconf.rb
creating Makefile

make
gcc -I. -I/usr/local/include/ruby-1.9.1/x86_64-linux -I/usr/local/include/ruby-1.9.1/ruby/backward -I/usr/local/include/ruby-1.9.1 -I.   -fPIC  -O2 -g -Wall -Wno-parentheses  -o system_timer_native.o -c system_timer_native.c
In file included from system_timer_native.c:8:
/usr/local/include/ruby-1.9.1/ruby/backward/rubysig.h:14:2: warning: #warning rubysig.h is obsolete
system_timer_native.c: In function ‘restore_original_configuration’:
system_timer_native.c:174: warning: no return statement in function returning non-void
system_timer_native.c: In function ‘install_ruby_sigalrm_handler’:
system_timer_native.c:207: error: ‘rb_thread_critical’ undeclared (first use in this function)
system_timer_native.c:207: error: (Each undeclared identifier is reported only once
system_timer_native.c:207: error: for each function it appears in.)
system_timer_native.c: In function ‘restore_original_ruby_sigalrm_handler’:
system_timer_native.c:213: error: ‘rb_thread_critical’ undeclared (first use in this function)
make: *** [system_timer_native.o] Error 1


Gem files will remain installed in /usr/local/lib/ruby/gems/1.9.1/gems/SystemTimer-1.2 for inspection.
Results logged to /usr/local/lib/ruby/gems/1.9.1/gems/SystemTimer-1.2/ext/system_timer/gem_make.out