diff --git a/sample_app/Gemfile b/sample_app/Gemfile
index a2f2ab7..01912b6 100644
--- a/sample_app/Gemfile
+++ b/sample_app/Gemfile
@@ -11,7 +11,7 @@ gem "kaminari"
 gem "mini_magick", "~> 4.8"
 gem "sidekiq", "~> 5.0", ">= 5.0.5"
 
-gem "puma", "~> 3.11"
+gem "puma", "~> 4.3"
 gem "rails", "~> 5.2.0"
 gem "sass-rails", "~> 5.0"
 gem "sqlite3"
diff --git a/sample_app/Gemfile.lock b/sample_app/Gemfile.lock
index fc6bd39..12a9b03 100644
--- a/sample_app/Gemfile.lock
+++ b/sample_app/Gemfile.lock
@@ -315,7 +315,9 @@ GEM
     mime-types (3.1)
       mime-types-data (~> 3.2015)
     mime-types-data (3.2016.0521)
-    mimemagic (0.3.2)
+    mimemagic (0.3.10)
+      nokogiri (~> 1)
+      rake
     mini_magick (4.8.0)
     mini_mime (1.0.0)
     mini_portile2 (2.3.0)
@@ -333,7 +335,8 @@ GEM
       ast (~> 2.4.0)
     popper_js (1.12.9)
     powerpack (0.1.2)
-    puma (3.11.4)
+    puma (4.3.9)
+      nio4r (~> 2.0)
     rack (2.0.5)
     rack-protection (2.0.3)
       rack
@@ -464,7 +467,7 @@ DEPENDENCIES
   kaminari
   listen (>= 3.0.5, < 3.2)
   mini_magick (~> 4.8)
-  puma (~> 3.11)
+  puma (~> 4.3)
   rails (~> 5.2.0)
   rubocop (~> 0.54.0)
   sass-rails (~> 5.0)