diff --git a/lita-tox.gemspec b/lita-tox.gemspec
index 6b32fde..c18f07f 100644
--- a/lita-tox.gemspec
+++ b/lita-tox.gemspec
@@ -21,6 +21,8 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
+  spec.extensions << 'ext/tox/extconf.rb'
+
   spec.add_development_dependency 'bundler', '~> 1.7'
   spec.add_development_dependency 'rake', '~> 10.0'
   spec.add_development_dependency 'rubocop', '~> 0.31'