diff --git a/fluent-plugin-sql.gemspec b/fluent-plugin-sql.gemspec
index 90d483f..be227d1 100644
--- a/fluent-plugin-sql.gemspec
+++ b/fluent-plugin-sql.gemspec
@@ -17,6 +17,7 @@ Gem::Specification.new do |gem|
   gem.license = "Apache-2.0"
 
   gem.add_dependency "fluentd", [">= 1.7.0", "< 2"]
+  gem.add_dependency "ostruct", '~> 0.6'
   gem.add_dependency 'activerecord', [">= 6.1", "< 7.2"]
   gem.add_dependency 'activerecord-import', "~> 1.0"
   gem.add_development_dependency "rake", ">= 0.9.2"