diff --git a/Gemfile b/Gemfile
index fdb38b9..3b1561f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -14,7 +14,7 @@ gem 'rails', '~> 5.1.2'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.12'
+gem 'puma', '~> 4.3', '>= 4.3.9'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
diff --git a/Gemfile.lock b/Gemfile.lock
index 4112671..b6c5ae1 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -96,7 +96,8 @@ GEM
       mini_portile2 (~> 2.4.0)
     pg (0.21.0)
     public_suffix (2.0.5)
-    puma (3.12.6)
+    puma (4.3.10)
+      nio4r (~> 2.0)
     rack (2.2.3)
     rack-test (0.6.3)
       rack (>= 1.0)
@@ -188,7 +189,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   listen (>= 3.0.5, < 3.2)
   pg
-  puma (~> 3.12)
+  puma (~> 4.3, >= 4.3.9)
   rails (~> 5.1.2)
   sass-rails (~> 5.0)
   selenium-webdriver
@@ -200,4 +201,4 @@ DEPENDENCIES
   web-console (>= 3.3.0)
 
 BUNDLED WITH
-   1.15.3
+   1.17.3