diff --git a/rdf.gemspec b/rdf.gemspec
index aaad04e4..59231efe 100755
--- a/rdf.gemspec
+++ b/rdf.gemspec
@@ -32,6 +32,7 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency     'link_header', '~> 0.0', '>= 0.0.8'
   gem.add_runtime_dependency     'bcp47_spec',  '~> 0.2'
   gem.add_runtime_dependency     'bigdecimal',  '~> 3.1', '>= 3.1.5'
+  gem.add_runtime_dependency     'ostruct',     '~> 0.6'
   gem.add_development_dependency 'base64',      '~> 0.2'
   gem.add_development_dependency 'rdf-spec',    '~> 3.3'
   gem.add_development_dependency 'rdf-turtle',  '~> 3.3'