diff --git a/Calculator/Gemfile b/Calculator/Gemfile
index 99f6cc4..bb1e542 100644
--- a/Calculator/Gemfile
+++ b/Calculator/Gemfile
@@ -11,7 +11,7 @@ gem 'rails', '~> 5.1.4'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.12'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
diff --git a/Calculator/Gemfile.lock b/Calculator/Gemfile.lock
index 7ddef05..c80c9fe 100644
--- a/Calculator/Gemfile.lock
+++ b/Calculator/Gemfile.lock
@@ -94,7 +94,8 @@ GEM
     nokogiri (1.10.4)
       mini_portile2 (~> 2.4.0)
     public_suffix (3.0.0)
-    puma (3.12.2)
+    puma (4.3.8)
+      nio4r (~> 2.0)
     rack (2.0.8)
     rack-test (0.7.0)
       rack (>= 1.0, < 3)
@@ -189,7 +190,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   listen (>= 3.0.5, < 3.2)
   nokogiri (~> 1.10.4)
-  puma (~> 3.12)
+  puma (~> 4.3)
   rails (~> 5.1.4)
   sass-rails (~> 5.0)
   selenium-webdriver