diff --git a/Gemfile b/Gemfile
index ed41580..7de4800 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 e94ad31..0fb47b1 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -82,7 +82,8 @@ GEM
     nio4r (2.5.2)
     nokogiri (1.10.9)
       mini_portile2 (~> 2.4.0)
-    puma (3.9.1)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.2.3)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -166,7 +167,7 @@ DEPENDENCIES
   jbuilder (= 2.6.4)
   jquery-rails (= 4.3.1)
   listen (= 3.1.5)
-  puma (= 3.9.1)
+  puma (= 4.3.12)
   rails (= 5.1.6)
   sass-rails (= 5.0.6)
   spring (= 2.0.2)