diff --git a/ext/json/json.gemspec b/ext/json/json.gemspec
index c714ba86d1..39b0155d46 100644
--- a/ext/json/json.gemspec
+++ b/ext/json/json.gemspec
@@ -50,6 +50,7 @@ Gem::Specification.new do |s|
     "lib/json/add/time.rb",
     "lib/json/common.rb",
     "lib/json/ext.rb",
+    "lib/json/ext/generator/state.rb",
     "lib/json/generic_object.rb",
     "lib/json/pure.rb",
     "lib/json/pure/generator.rb",