diff -u -r ../ruby-2.3.0/tool/rbinstall.rb ./tool/rbinstall.rb
--- ../ruby-2.3.0/tool/rbinstall.rb    2015-11-16 01:33:17.000000000 -0500
+++ ./tool/rbinstall.rb        2015-12-25 15:43:04.756646343 -0500
@@ -696,7 +696,7 @@
 # :startdoc:

 install?(:ext, :comm, :gem) do
-  gem_dir = Gem.default_dir
+  gem_dir = "@TERMUX_PREFIX@/lib/ruby/gems/2.4.0"
   directories = Gem.ensure_gem_subdirectories(gem_dir, :mode => $dir_mode)
   prepare "default gems", gem_dir, directories

@@ -732,7 +732,7 @@
 end

 install?(:ext, :comm, :gem) do
-  gem_dir = Gem.default_dir
+  gem_dir = "@TERMUX_PREFIX@/lib/ruby/gems/2.4.0"
   directories = Gem.ensure_gem_subdirectories(gem_dir, :mode => $dir_mode)
   prepare "bundle gems", gem_dir, directories
   install_dir = with_destdir(gem_dir)