diff --git a/lib/mruby/gem.rb b/lib/mruby/gem.rb
index 0be0ada35..64c6f3dee 100644
--- a/lib/mruby/gem.rb
+++ b/lib/mruby/gem.rb
@@ -170,7 +170,7 @@ module MRuby
       end
 
       def funcname
-        @funcname ||= @name.gsub('-', '_')
+        @funcname ||= @name.tr('-', '_')
       end
 
       def compilers
diff --git a/test/bintest.rb b/test/bintest.rb
index 773d61edc..ca6bb8e5d 100644
--- a/test/bintest.rb
+++ b/test/bintest.rb
@@ -44,7 +44,7 @@ ARGV.each do |gem|
 
   case RbConfig::CONFIG['host_os']
   when /mswin(?!ce)|mingw|bccwin/
-    gem = gem.gsub('\\', '/')
+    gem = gem.tr('\\', '/')
   end
 
   Dir["#{gem}/bintest/**/*.rb"].each do |file|