diff --git a/demo/Gemfile b/demo/Gemfile
index a6e4892..337247f 100644
--- a/demo/Gemfile
+++ b/demo/Gemfile
@@ -11,7 +11,7 @@ gem 'rails', '~> 5.0.7', '>= 5.0.7.2'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3', '~> 1.3.11'
 # Use Puma as the app server
-gem 'puma', '~> 3.0'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
diff --git a/demo/Gemfile.lock b/demo/Gemfile.lock
index 0688697..3716637 100644
--- a/demo/Gemfile.lock
+++ b/demo/Gemfile.lock
@@ -117,7 +117,8 @@ GEM
     pry (0.13.0)
       coderay (~> 1.1)
       method_source (~> 1.0)
-    puma (3.12.4)
+    puma (4.3.8)
+      nio4r (~> 2.0)
     rack (2.2.2)
     rack-test (0.6.3)
       rack (>= 1.0)
@@ -209,7 +210,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   jquery-rails
   listen (~> 3.0.5)
-  puma (~> 3.0)
+  puma (~> 4.3)
   rails (~> 5.0.7, >= 5.0.7.2)
   sass-rails (~> 5.0)
   simple_form (~> 5.0, >= 5.0.2)