diff --git a/Gemfile b/Gemfile
index c4ab786..ba5ad44 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,7 +7,7 @@ gem 'rails', '~> 5.0.0', '>= 5.0.0.1'
 gem 'sqlite3', group: :development
 gem 'pg', group: :production
 # 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 b5d7a74..51e87a5 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -143,7 +143,8 @@ GEM
     orm_adapter (0.5.0)
     pg (0.20.0)
     public_suffix (2.0.5)
-    puma (3.12.6)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     pygments.rb (1.1.2)
       multi_json (>= 1.0.0)
     qiita-markdown (0.20.1)
@@ -284,7 +285,7 @@ DEPENDENCIES
   less-rails
   listen (~> 3.0.5)
   pg
-  puma (~> 3.12)
+  puma (~> 4.3)
   qiita-markdown
   rails (~> 5.0.0, >= 5.0.0.1)
   rails_admin