diff --git a/Gemfile b/Gemfile
index 4682586..b21e279 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,7 +1,7 @@
 source 'https://rubygems.org'
 
 gem 'rails',        '5.1.6'
-gem 'puma',         '3.9.1'
+gem 'puma',         '4.3.12'
 gem 'sass-rails',   '5.0.6'
 gem 'uglifier',     '3.2.0'
 gem 'coffee-rails', '4.2.2'
diff --git a/Gemfile.lock b/Gemfile.lock
index 2fa1075..ab369bc 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -112,7 +112,8 @@ GEM
     pry (0.12.2)
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
-    puma (3.9.1)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -207,7 +208,7 @@ DEPENDENCIES
   minitest (= 5.10.3)
   minitest-reporters (= 1.1.14)
   pg (= 0.20.0)
-  puma (= 3.9.1)
+  puma (= 4.3.12)
   rails (= 5.1.6)
   rails-controller-testing (= 1.0.2)
   sass-rails (= 5.0.6)