diff --git a/Gemfile b/Gemfile
index b13895a..4e046f9 100644
--- a/Gemfile
+++ b/Gemfile
@@ -2,7 +2,7 @@ source 'https://rubygems.org'
 ruby '2.4.1'
 
 # HTTP server for Ruby/Rack recommended by Heroku
-gem 'puma', '~> 3.11'
+gem 'puma', '~> 4.1'
 
 # Middleman
 gem 'middleman', '~> 4.2', '>= 4.2.1'
diff --git a/Gemfile.lock b/Gemfile.lock
index 6a9b5f5..02e8162 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -89,6 +89,7 @@ GEM
       middleman-core (>= 3.2)
       rouge (~> 2.0)
     minitest (5.11.3)
+    nio4r (2.5.1)
     padrino-helpers (0.13.3.4)
       i18n (~> 0.6, >= 0.6.7)
       padrino-support (= 0.13.3.4)
@@ -97,7 +98,8 @@ GEM
       activesupport (>= 3.1)
     parallel (1.12.1)
     public_suffix (3.0.2)
-    puma (3.11.3)
+    puma (4.1.1)
+      nio4r (~> 2.0)
     rack (1.6.10)
     rack-contrib (1.8.0)
       rack (~> 1.4)
@@ -135,7 +137,7 @@ DEPENDENCIES
   middleman-livereload (~> 3.4, >= 3.4.6)
   middleman-sprockets (~> 4.1)
   middleman-syntax (= 3.0.0)
-  puma (~> 3.11)
+  puma (~> 4.1)
   rack-contrib (~> 1.5)
   redcarpet (= 3.4.0)
   slim (~> 3.0, >= 3.0.8)