diff --git a/w5d4/demo_project/Gemfile b/w5d4/demo_project/Gemfile
index 8f784732..727762f6 100644
--- a/w5d4/demo_project/Gemfile
+++ b/w5d4/demo_project/Gemfile
@@ -11,7 +11,7 @@ gem 'rails', '~> 5.1.2'
 # Use sqlite3 as the database for Active Record
 gem 'pg'
 # Use Puma as the app server
-gem 'puma', '~> 3.7'
+gem 'puma', '~> 4.3'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
diff --git a/w5d4/demo_project/Gemfile.lock b/w5d4/demo_project/Gemfile.lock
index d0aa3135..961f2b5e 100644
--- a/w5d4/demo_project/Gemfile.lock
+++ b/w5d4/demo_project/Gemfile.lock
@@ -104,7 +104,8 @@ GEM
     pry-rails (0.3.9)
       pry (>= 0.10.4)
     public_suffix (4.0.5)
-    puma (3.12.6)
+    puma (4.3.9)
+      nio4r (~> 2.0)
     rack (2.2.2)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
@@ -197,7 +198,7 @@ DEPENDENCIES
   listen (>= 3.0.5, < 3.2)
   pg
   pry-rails
-  puma (~> 3.7)
+  puma (~> 4.3)
   rails (~> 5.1.2)
   sass-rails (~> 5.0)
   selenium-webdriver