diff --git a/Gemfile b/Gemfile
index 3b39d289..22b61e05 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,6 +1,7 @@
 source 'https://rubygems.org'
 ruby "~> 2.6"
 
+gem 'ffi', '=1.16.3'
 gem 'github-pages'
 gem 'rouge'
 gem "webrick", "~> 1.7"