diff --git a/Gemfile b/Gemfile
index 77748f77..0cec8eb2 100644
--- a/Gemfile
+++ b/Gemfile
@@ -15,7 +15,7 @@ gem 'sdoc', '~> 0.4.0', group: :doc
 
 gem 'rack-cache'
 gem 'bcrypt', '~> 3.1.7'
-gem 'puma', '~> 3.2'
+gem 'puma', '~> 4.3'
 gem 'rails_12factor'
 
 gem 'simple_form', '~> 3.2'
diff --git a/Gemfile.lock b/Gemfile.lock
index 528a83d1..87f29f2e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -133,6 +133,7 @@ GEM
     minitest (5.9.0)
     multi_xml (0.5.5)
     nenv (0.3.0)
+    nio4r (2.5.2)
     nokogiri (1.6.8)
       mini_portile2 (~> 2.1.0)
       pkg-config (~> 1.1.7)
@@ -151,7 +152,8 @@ GEM
       coderay (~> 1.1.0)
       method_source (~> 0.8.1)
       slop (~> 3.4)
-    puma (3.4.0)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (1.6.4)
     rack-cache (1.6.1)
       rack (>= 0.4)
@@ -292,7 +294,7 @@ DEPENDENCIES
   letter_opener
   pg (~> 0.15)
   premailer-rails
-  puma (~> 3.2)
+  puma (~> 4.3)
   rack-cache
   rails (= 4.2.5.1)
   rails_12factor