diff --git a/Gemfile b/Gemfile
index e80c9fd..b8a1618 100644
--- a/Gemfile
+++ b/Gemfile
@@ -12,7 +12,7 @@ gem 'rails', '~> 5.1.7'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'
 # 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/Gemfile.lock b/Gemfile.lock
index 659bda4..35dd4e2 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -502,7 +502,8 @@ GEM
     power_converter (0.1.2)
     public_suffix (3.1.1)
     pul_uv_rails (2.0.1)
-    puma (3.12.1)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     qa (2.2.0)
       activerecord-import
       deprecation
@@ -772,7 +773,7 @@ DEPENDENCIES
   jbuilder (~> 2.5)
   jquery-rails
   listen (>= 3.0.5, < 3.2)
-  puma (~> 3.7)
+  puma (~> 4.3)
   rails (~> 5.1.7)
   riiif (~> 2.0)
   rsolr (>= 1.0)