diff --git a/Rakefile b/Rakefile
index 8432bb83c..db6cbf91a 100644
--- a/Rakefile
+++ b/Rakefile
@@ -10,7 +10,7 @@ Rake.verbose(false) if Rake.verbose == Rake::DSL::DEFAULT
 $LOAD_PATH << File.join(MRUBY_ROOT, "lib")
 
 # load build systems
-require "mruby-core-ext"
+require "mruby/core_ext"
 require "mruby/build"
 
 # load configuration file
diff --git a/lib/mruby/build.rb b/lib/mruby/build.rb
index 4ae3a6c53..59b5cd583 100644
--- a/lib/mruby/build.rb
+++ b/lib/mruby/build.rb
@@ -1,4 +1,4 @@
-require "mruby-core-ext"
+require "mruby/core_ext"
 require "mruby/build/load_gems"
 require "mruby/build/command"
 
diff --git a/lib/mruby-core-ext.rb b/lib/mruby/core_ext.rb
similarity index 100%
rename from lib/mruby-core-ext.rb
rename to lib/mruby/core_ext.rb