diff --git a/Gemfile b/Gemfile
index 6581874..773471b 100644
--- a/Gemfile
+++ b/Gemfile
@@ -8,7 +8,7 @@ gem 'rails', '~> 5.2.3'
 # Use postgresql as the database for Active Record
 gem 'pg', '>= 0.18', '< 2.0'
 # 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/Gemfile.lock b/Gemfile.lock
index 9011b0d..f80dbae 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,6 +1,10 @@
 GEM
-  remote: https://rubygems.org/
   remote: https://rails-assets.org/
+  specs:
+    rails-assets-tether (1.4.7)
+
+GEM
+  remote: https://rubygems.org/
   specs:
     actioncable (5.2.3)
       actionpack (= 5.2.3)
@@ -170,7 +174,8 @@ GEM
     pg (1.1.4)
     popper_js (1.11.1)
     public_suffix (3.1.1)
-    puma (3.12.2)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -187,7 +192,6 @@ GEM
       bundler (>= 1.3.0)
       railties (= 5.2.3)
       sprockets-rails (>= 2.0.0)
-    rails-assets-tether (1.4.7)
     rails-dom-testing (2.0.3)
       activesupport (>= 4.2.0)
       nokogiri (>= 1.6)
@@ -300,7 +304,7 @@ DEPENDENCIES
   mini_racer
   pg (>= 0.18, < 2.0)
   popper_js (~> 1.11.1)
-  puma (~> 3.12)
+  puma (~> 4.3)
   rails (~> 5.2.3)
   rails-assets-tether (>= 1.3.3)!
   rspec-rails (~> 3.5)