diff --git a/lib/pathname.rb b/lib/pathname.rb
index 9a29752..d8fe335 100644
--- a/lib/pathname.rb
+++ b/lib/pathname.rb
@@ -544,6 +544,19 @@ def relative_path_from(base_directory)
       Pathname.new(File.join(*relpath_names))
     end
   end
+
+  # Return a pathname whose basename is substituted by String#sub.
+  #
+  #     path1 = Pathname.new('/usr/bin/perl')
+  #     path1.basename_sub('perl', 'ruby')
+  #         #=> #<Pathname:/usr/bin/ruby>
+  #     path1.basename_sub(/\Aperl\z/, 'ruby')
+  #         #=> #<Pathname:/usr/bin/ruby>
+  #
+  def basename_sub(pattern, replacement)
+    dir, base = split
+    dir + base.sub(pattern, replacement)
+  end
 end
 
 
@@ -597,4 +610,3 @@ def rmtree(noop: nil, verbose: nil, secure: nil)
     nil
   end
 end
-
diff --git a/test/pathname/test_pathname.rb b/test/pathname/test_pathname.rb
index a23dc21..c110a17 100644
--- a/test/pathname/test_pathname.rb
+++ b/test/pathname/test_pathname.rb
@@ -557,6 +557,15 @@ def test_comparison_string
 
   def pathsub(path, pat, repl) Pathname.new(path).sub(pat, repl).to_s end
   defassert(:pathsub, "a.o", "a.c", /\.c\z/, ".o")
+  defassert(:pathsub, "bar/bar", "bar/foo", "foo", "bar")
+
+  def pathbasesub(path, pat, repl) Pathname.new(path).basename_sub(pat, repl).to_s end
+  defassert(:pathbasesub, "a.o", "a.c", /\.c\z/, ".o")
+  defassert(:pathbasesub, "bar", "foo", "foo", "bar")
+  defassert(:pathbasesub, "bar", "foo", /\Afoo\z/, "bar")
+  defassert(:pathbasesub, "foo/bar", "foo/foo", "foo", "bar")
+  defassert(:pathbasesub, "foo/bar", "foo/foo", /\Afoo\z/, "bar")
+  defassert(:pathbasesub, "foo/fofo", "foo/foo", /\A(fo)o\z/, '\1\1')
 
   def pathsubext(path, repl) Pathname.new(path).sub_ext(repl).to_s end
   defassert(:pathsubext, 'a.o', 'a.c', '.o')