diff --git a/autoprefixer-rails.gemspec b/autoprefixer-rails.gemspec
index 6984093..90c210c 100644
--- a/autoprefixer-rails.gemspec
+++ b/autoprefixer-rails.gemspec
@@ -20,7 +20,8 @@ Gem::Specification.new do |s|
   s.homepage = "https://github.com/ai/autoprefixer-rails"
   s.license  = "MIT"
 
-  s.add_dependency "execjs", ">= 0"
+  # see #203, `process` is undefined in 2.8
+  s.add_dependency "execjs", "< 2.8.0"
 
   s.add_development_dependency "rails"
   s.add_development_dependency "rake"