diff --git a/Gemfile b/Gemfile
index fb5bd36..4b71a07 100644
--- a/Gemfile
+++ b/Gemfile
@@ -11,3 +11,4 @@ gem 'nokogiri'
 gem 'numo-narray'
 gem 'i18n'
 gem 'gruff'
+gem 'net-http' # to avoid error: uninitialized constant ...