diff --git a/Gemfile b/Gemfile
index d7e07a97a9a873b00a8235ee8a442fe76f00041f..33b2ef6f10ed49d24743df1ddee342e4166d5682 100644
--- a/Gemfile
+++ b/Gemfile
@@ -10,6 +10,7 @@ gem 'bcrypt'
 gem 'unicorn'
 gem 'pony'
 gem 'rest-client'
+gem 'rack', '2.2.3'
 gem 'rack-cas'
 gem 'icalendar'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index bdc578cd5df2c35c092cbbd8c23ed6a55b4702d9..903c6f1fb5237f88353d0245a12c9d5b2c577c8e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -81,7 +81,7 @@ GEM
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     public_suffix (4.0.3)
-    rack (2.1.1)
+    rack (2.2.3)
     rack-cas (0.16.1)
       addressable (~> 2.3)
       nokogiri (~> 1.5)
@@ -145,6 +145,7 @@ DEPENDENCIES
   icalendar
   mysql2
   pony
+  rack (= 2.2.3)
   rack-cas
   rest-client
   shotgun