diff --git a/gollum.gemspec b/gollum.gemspec
index c2dd2900..192cde1e 100644
--- a/gollum.gemspec
+++ b/gollum.gemspec
@@ -25,6 +25,7 @@ Gem::Specification.new do |s|
   s.add_dependency('grit', "~> 2.4.1")
   s.add_dependency('github-markup', [">= 0.4.0", "< 1.0.0"])
   s.add_dependency('pygments.rb', "~> 0.2.0")
+  s.add_dependency('posix-spawn', "~> 0.3.0")
   s.add_dependency('sinatra', "~> 1.0")
   s.add_dependency('mustache', [">= 0.11.2", "< 1.0.0"])
   s.add_dependency('sanitize', "~> 2.0.0")