diff --git a/study_guides/rails/99cats_debugger/Gemfile b/study_guides/rails/99cats_debugger/Gemfile
index 0727aa77a..361bb827c 100644
--- a/study_guides/rails/99cats_debugger/Gemfile
+++ b/study_guides/rails/99cats_debugger/Gemfile
@@ -11,7 +11,7 @@ gem 'rails', '~> 5.2.0'
 # Use postgresql as the database for Active Record
 gem 'pg', '>= 1.0.0'
 # Use Puma as the app server
-gem 'puma', '~> 4.3'
+gem 'puma', '~> 5.6'
 # Use SCSS for stylesheets
 gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
diff --git a/study_guides/rails/99cats_debugger/Gemfile.lock b/study_guides/rails/99cats_debugger/Gemfile.lock
index d341faf47..b5574e26c 100644
--- a/study_guides/rails/99cats_debugger/Gemfile.lock
+++ b/study_guides/rails/99cats_debugger/Gemfile.lock
@@ -102,7 +102,7 @@ GEM
     mini_mime (1.0.2)
     mini_portile2 (2.4.0)
     minitest (5.11.3)
-    nio4r (2.5.2)
+    nio4r (2.5.9)
     nokogiri (1.10.9)
       mini_portile2 (~> 2.4.0)
     pg (1.1.4)
@@ -112,7 +112,7 @@ GEM
     pry-rails (0.3.9)
       pry (>= 0.10.4)
     public_suffix (3.1.1)
-    puma (4.3.5)
+    puma (5.6.7)
       nio4r (~> 2.0)
     rack (2.2.3)
     rack-test (1.1.0)
@@ -205,7 +205,7 @@ DEPENDENCIES
   listen (>= 3.0.5, < 3.2)
   pg (>= 1.0.0)
   pry-rails
-  puma (~> 4.3)
+  puma (~> 5.6)
   rails (~> 5.2.0)
   sass-rails (~> 5.0)
   selenium-webdriver