diff --git a/Training/to_do_list/Gemfile b/Training/to_do_list/Gemfile
index 21c0414..18facda 100644
--- a/Training/to_do_list/Gemfile
+++ b/Training/to_do_list/Gemfile
@@ -8,7 +8,7 @@ gem 'rails', '~> 5.2.2', '>= 5.2.2.1'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.11'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
diff --git a/Training/to_do_list/Gemfile.lock b/Training/to_do_list/Gemfile.lock
index 1af2011..68875c0 100644
--- a/Training/to_do_list/Gemfile.lock
+++ b/Training/to_do_list/Gemfile.lock
@@ -105,7 +105,8 @@ GEM
     nokogiri (1.10.9)
       mini_portile2 (~> 2.4.0)
     public_suffix (4.0.4)
-    puma (3.12.4)
+    puma (4.3.9)
+      nio4r (~> 2.0)
     rack (2.2.2)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -199,7 +200,7 @@ DEPENDENCIES
   coffee-rails (~> 4.2)
   jbuilder (~> 2.5)
   listen (>= 3.0.5, < 3.2)
-  puma (~> 3.11)
+  puma (~> 4.3)
   rails (~> 5.2.2, >= 5.2.2.1)
   sass-rails (~> 5.0)
   selenium-webdriver