diff --git a/rb/selenium-webdriver.gemspec b/rb/selenium-webdriver.gemspec
index 35349a72a9129..954899e6d2941 100644
--- a/rb/selenium-webdriver.gemspec
+++ b/rb/selenium-webdriver.gemspec
@@ -49,6 +49,7 @@ Gem::Specification.new do |s|
   s.bindir = 'bin'
   s.require_paths = ['lib']
 
+  s.add_runtime_dependency 'base64'
   s.add_runtime_dependency 'rexml', ['~> 3.2', '>= 3.2.5']
   s.add_runtime_dependency 'rubyzip', ['>= 1.2.2', '< 3.0']
   s.add_runtime_dependency 'websocket', ['~> 1.0']