diff --git a/Gemfile b/Gemfile
index c05ba55..bb813c3 100644
--- a/Gemfile
+++ b/Gemfile
@@ -17,7 +17,7 @@ gem 'rails-i18n', '~> 6.0.0.beta1'
 gem 'pg', '>= 0.18', '< 2.0'
 
 # Use Puma as the app server.
-gem 'puma', '~> 3.11'
+gem 'puma', '~> 4.0'
 
 # Use Uglifier as compressor for JavaScript assets.
 gem 'uglifier', '>= 1.3.0'
diff --git a/Gemfile.lock b/Gemfile.lock
index bd791cc..a70ac07 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -258,7 +258,8 @@ GEM
       pry (>= 0.10.4)
     psych (3.1.0)
     public_suffix (3.1.1)
-    puma (3.12.1)
+    puma (4.0.0)
+      nio4r (~> 2.0)
     pundit (2.0.1)
       activesupport (>= 3.0.0)
     pundit-matchers (1.6.0)
@@ -475,7 +476,7 @@ DEPENDENCIES
   pg (>= 0.18, < 2.0)
   pry-doc (~> 1.0)
   pry-rails (~> 0.3)
-  puma (~> 3.11)
+  puma (~> 4.0)
   pundit (~> 2.0)
   pundit-matchers (~> 1.6)
   rack-attack (~> 5.4)