diff --git a/Gemfile b/Gemfile
index b56578b3..ab1e7922 100644
--- a/Gemfile
+++ b/Gemfile
@@ -19,6 +19,7 @@ gem 'sass-rails', '>= 5'
 # https://gihyo.jp/article/2024/01/ruby3.3-bundled-gems
 gem 'csv'
 gem 'ostruct' # Depended by 'koala' gem and shown at 'deploy' job in Actions (rake assets:precompile)
+gem 'openssl' # Avoid version mismatch with system OpenSSL
 
 gem 'rambulance'         # Error handling pages: https://github.com/yuki24/rambulance
 gem 'airbrake'           # Error Monitoring by Airbrake: https://github.com/airbrake/airbrake
diff --git a/Gemfile.lock b/Gemfile.lock
index 667b5d31..af98c72a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -265,6 +265,7 @@ GEM
     nokogiri (1.18.9-x86_64-linux-musl)
       racc (~> 1.4)
     observer (0.1.2)
+    openssl (3.3.2)
     ostruct (0.6.1)
     parallel (1.27.0)
     parser (3.3.8.0)
@@ -509,6 +510,7 @@ DEPENDENCIES
   letter_opener_web
   listen
   memory_profiler
+  openssl
   ostruct
   pg
   puma