Cannot install Puma gem on Ruby on Rails

I'm trying to install the puma gem, but when I run ``` gem install puma ``` I get this error message: ``` Temporarily enhancing PATH to include DevKit Building native extensions. This could take a while... ERROR: Error installing puma: ERROR: Failed to build gem native extension. C:/Ruby193/bin/ruby.exe extconf.rb creating Makefile make generating puma_http11-i386-mingw32.def compiling http11_parser.c ext/http11/http11_parser.rl: In function 'puma_parser_execute': ext/http11/http11_parser.rl:111:3: warning: comparison between signed and unsigned integer expressions compiling io_buffer.c io_buffer.c: In function 'buf_to_str': io_buffer.c:119:3: warning: pointer targets in passing argument 1 of 'rb_str_new' differ in signedness c:/Ruby193/include/ruby-1.9.1/ruby/intern.h:653:7: note: expected 'const char *' but argument is of type 'uint8_t *' compiling mini_ssl.c In file included from mini_ssl.c:3:0: c:/Ruby193/include/ruby-1.9.1/ruby/backward/rubyio.h:2:2: warning: #warning use "ruby/io.h" instead of "rubyio.h" mini_ssl.c:4:25: fatal error: openssl/bio.h: No such file or directory compilation terminated. make: *** [mini_ssl.o] Error 1 Gem files will remain installed in C:/Ruby193/lib/ruby/gems/1.9.1/gems/puma-2.6.0 for inspection. Results logged to C:/Ruby193/lib/ruby/gems/1.9.1/gems/puma-2.6.0/ext/puma_http11/gem_make.out ``` Adding `gem 'puma'` to my Gemfile and running `bundle install` isn't an option, because that just doesn't work with any gem and gives me an error message (which is a separate issue, one that I've circumvented with the other gems I've used by installing them via `gem install`).