diff --git a/Gemfile b/Gemfile
index a468984..cc36f78 100644
--- a/Gemfile
+++ b/Gemfile
@@ -12,7 +12,7 @@ gem 'rails', '~> 5.1.7'
 gem 'mysql2', '>= 0.3.18', '< 0.6.0'
 # gem "mysql2", "~> 0.4.0"
 # 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 fed8682..1056feb 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -193,7 +193,8 @@ GEM
       coderay (~> 1.1)
       method_source (~> 1.0)
     public_suffix (4.0.6)
-    puma (3.12.6)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     raabro (1.4.0)
     racc (1.5.2)
     rack (2.2.3)
@@ -336,7 +337,7 @@ DEPENDENCIES
   mysql2 (>= 0.3.18, < 0.6.0)
   ontologies_api_client!
   pry
-  puma (~> 3.7)
+  puma (~> 4.3)
   rails (~> 5.1.7)
   rest-client
   rubocop