diff --git a/README.md b/README.md
index ed7216c..930f5d1 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 [<img src="https://travis-ci.org/dougfales/gpx.svg" alt="Build Status" />](https://travis-ci.org/dougfales/gpx)
 [![Code Climate](https://codeclimate.com/github/dougfales/gpx/badges/gpa.svg)](https://codeclimate.com/github/dougfales/gpx)
 
-Copyright (C) 2006 Doug Fales doug@falesafeconsulting.com 
+Copyright (C) 2006 Doug Fales doug@falesafeconsulting.com
 
 Released under the MIT License.
 
@@ -19,9 +19,14 @@ rectangular areas within a file, and it also calculates some meta-data about
 the tracks and points in a file (such as distance, duration, average speed,
 etc).
 
+## Requirements
+
+As of `0.9.0`, `gpx` requires at least Ruby 2.1 to run.
+
 ## Examples
 
 Reading a GPX file, and cropping its contents to a given area:
+
 ```ruby
 gpx =  GPX::GPXFile.new(:gpx_file => filename)   # Read GPX file
 bounds = GPX::Bounds.new(params)                 # Create a rectangular area to crop
diff --git a/gpx.gemspec b/gpx.gemspec
index 334042b..0b8a1ec 100644
--- a/gpx.gemspec
+++ b/gpx.gemspec
@@ -11,6 +11,8 @@ Gem::Specification.new do |s|
   s.summary = %q{A basic API for reading and writing GPX files.}
   s.description = %q{A basic API for reading and writing GPX files.}
 
+  s.required_ruby_version = '~>2.1'
+
   s.files = `git ls-files`.split($/)
   s.test_files    = s.files.grep(%r{^(test|spec|features)/})
   s.require_paths = ["lib"]
@@ -18,7 +20,7 @@ Gem::Specification.new do |s|
 
   s.homepage = "http://www.github.com/dougfales/gpx"
   s.add_dependency 'rake'
-  s.add_dependency 'nokogiri'
+  s.add_dependency 'nokogiri', '~>1.7'
   s.add_development_dependency 'bundler'
   s.add_development_dependency 'minitest'
 end