diff --git a/lib/rscons.rb b/lib/rscons.rb
index 6a978a4..9e05eb4 100644
--- a/lib/rscons.rb
+++ b/lib/rscons.rb
@@ -4,8 +4,6 @@ require "rscons/environment"
 require "rscons/varset"
 require "rscons/version"
 
-require "rscons/monkey/string"
-
 # default builders
 require "rscons/builders/library"
 require "rscons/builders/object"
@@ -43,4 +41,11 @@ module Rscons
   def self.absolute_path?(path)
     path =~ %r{^(/|\w:[\\/])}
   end
+
+  # Return a new path by changing the suffix in path to suffix.
+  # @param path [String] the path to alter
+  # @param suffix [String] the new filename suffix
+  def self.set_suffix(path, suffix)
+    path.sub(/\.[^.]*$/, suffix)
+  end
 end
diff --git a/lib/rscons/builders/object.rb b/lib/rscons/builders/object.rb
index 05d02c0..3ba0fa3 100644
--- a/lib/rscons/builders/object.rb
+++ b/lib/rscons/builders/object.rb
@@ -55,7 +55,7 @@ module Rscons
         vars = vars.merge({
           '_TARGET' => target,
           '_SOURCES' => sources,
-          '_DEPFILE' => target.set_suffix('.mf'),
+          '_DEPFILE' => Rscons.set_suffix(target, '.mf'),
         })
         com_prefix = KNOWN_SUFFIXES.find do |compiler, suffix_var|
           sources.first.end_with?(*env[suffix_var])
diff --git a/lib/rscons/environment.rb b/lib/rscons/environment.rb
index 1d59cc1..28d6a89 100644
--- a/lib/rscons/environment.rb
+++ b/lib/rscons/environment.rb
@@ -102,7 +102,7 @@ module Rscons
     # Return the file name to be built from source_fname with suffix suffix.
     # This method takes into account the Environment's build directories.
     def get_build_fname(source_fname, suffix)
-      build_fname = source_fname.set_suffix(suffix).gsub('\\', '/')
+      build_fname = Rscons.set_suffix(source_fname, suffix).gsub('\\', '/')
       found_match = @build_dirs.find do |src_dir, obj_dir|
         if src_dir.is_a?(Regexp)
           build_fname.sub!(src_dir, obj_dir)
diff --git a/lib/rscons/monkey/string.rb b/lib/rscons/monkey/string.rb
deleted file mode 100644
index dc1f629..0000000
--- a/lib/rscons/monkey/string.rb
+++ /dev/null
@@ -1,9 +0,0 @@
-# Standard Ruby String class.
-class String
-  # Return a new string with the suffix (dot character and extension) changed
-  # to the given suffix.
-  # @param suffix [String] The new suffix.
-  def set_suffix(suffix = '')
-    sub(/\.[^.]*$/, suffix)
-  end
-end