diff --git a/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile b/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile
index be167fc..2d053f8 100644
--- a/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile
+++ b/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile
@@ -14,7 +14,7 @@ gem 'rails', '~> 5.1.4'
 # Use mysql as the database for Active Record
 gem 'mysql2', '>= 0.3.18', '< 0.5'
 # Use Puma as the app server
-gem 'puma', '~> 3.12'
+gem 'puma', '~> 4.3'
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
 # gem 'jbuilder', '~> 2.5'
 # Use ActiveModel has_secure_password
diff --git a/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile.lock b/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile.lock
index 7d11541..eadf964 100644
--- a/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile.lock
+++ b/2017-01-29-deep-dive-into-database-timeouts-in-rails/Gemfile.lock
@@ -66,7 +66,8 @@ GEM
     nio4r (2.1.0)
     nokogiri (1.10.8)
       mini_portile2 (~> 2.4.0)
-    puma (3.12.6)
+    puma (4.3.11)
+      nio4r (~> 2.0)
     rack (2.2.3)
     rack-test (0.7.0)
       rack (>= 1.0, < 3)
@@ -125,7 +126,7 @@ DEPENDENCIES
   byebug
   listen (>= 3.0.5, < 3.2)
   mysql2 (>= 0.3.18, < 0.5)
-  puma (~> 3.12)
+  puma (~> 4.3)
   rails (~> 5.1.4)
   spring
   spring-watcher-listen (~> 2.0.0)