diff --git a/Chapter02/pichat-api-attachments-service/Gemfile b/Chapter02/pichat-api-attachments-service/Gemfile
index 0466437..a9511bc 100644
--- a/Chapter02/pichat-api-attachments-service/Gemfile
+++ b/Chapter02/pichat-api-attachments-service/Gemfile
@@ -11,7 +11,7 @@ gem 'rails', '~> 5.1.4'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # Use Puma as the app server
-gem 'puma', '~> 3.7'
+gem 'puma', '~> 4.3'
 # Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
 # gem 'jbuilder', '~> 2.5'
 # Use Redis adapter to run Action Cable in production
diff --git a/Chapter02/pichat-api-attachments-service/Gemfile.lock b/Chapter02/pichat-api-attachments-service/Gemfile.lock
index e7997df..ac3f348 100644
--- a/Chapter02/pichat-api-attachments-service/Gemfile.lock
+++ b/Chapter02/pichat-api-attachments-service/Gemfile.lock
@@ -95,7 +95,8 @@ GEM
     nio4r (2.1.0)
     nokogiri (1.8.1)
       mini_portile2 (~> 2.3.0)
-    puma (3.10.0)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.0.3)
     rack-test (0.7.0)
       rack (>= 1.0, < 3)
@@ -179,7 +180,7 @@ DEPENDENCIES
   fog-google (= 0.6.0)
   jwt (~> 2.1.0)
   listen (>= 3.0.5, < 3.2)
-  puma (~> 3.7)
+  puma (~> 4.3)
   rails (~> 5.1.4)
   rspec-rails (~> 3.5)
   shoulda-matchers (~> 3.1)