diff --git a/Gemfile b/Gemfile
index 7e9fb9f5..78307e1c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,7 +7,7 @@ gem 'sequel'
 gem 'bcrypt'
 gem 'sinatra-flash',      require: 'sinatra/flash'
 gem 'sinatra-xsendfile',  require: 'sinatra/xsendfile'
-gem 'puma',               require: nil
+gem 'puma', '5.6.5',      require: nil
 gem 'rmagick',            require: nil
 gem 'sidekiq', '~> 5.2.0'
 gem 'mail'
diff --git a/Gemfile.lock b/Gemfile.lock
index 17b458fe..19a2042d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -198,7 +198,7 @@ GEM
       coderay (~> 1.1)
       method_source (~> 1.0)
     public_suffix (5.0.0)
-    puma (6.0.0)
+    puma (5.6.5)
       nio4r (~> 2.0)
     racc (1.6.0)
     rack (2.2.4)
@@ -352,7 +352,7 @@ DEPENDENCIES
   paypal-recurring
   pg
   pry
-  puma
+  puma (= 5.6.5)
   rack-cache
   rack-test
   rack_session_access