diff --git a/Gemfile b/Gemfile
index bfd6301..3cf0e75 100644
--- a/Gemfile
+++ b/Gemfile
@@ -41,6 +41,10 @@ gem 'cancancan'
 
 gem 'nokogiri'
 
+# FFI 1.17+ isn't compatible with Ruby 2.x on Linux, which breaks GitHub Actions.
+# Remove this line when upgrading to Ruby 3.
+gem 'ffi', '~> 1.16.3'
+
 group :development, :test do
   gem 'ffaker'
   gem 'ruby-progressbar', require: false
diff --git a/Gemfile.lock b/Gemfile.lock
index 06aeed7..a94501d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -88,7 +88,7 @@ GEM
     fancybox2-rails (0.2.7)
       railties (>= 3.1.0)
     ffaker (2.21.0)
-    ffi (1.17.0)
+    ffi (1.16.3)
     ffi-compiler (1.3.2)
       ffi (>= 1.15.5)
       rake
@@ -289,6 +289,7 @@ DEPENDENCIES
   factory_bot_rails
   fancybox2-rails
   ffaker
+  ffi (~> 1.16.3)
   formtastic
   haml (~> 5.0)
   icalendar (~> 2.4)