diff --git a/son-gtkmano/Gemfile b/son-gtkmano/Gemfile
index c7a57e1c..3e6f1c27 100644
--- a/son-gtkmano/Gemfile
+++ b/son-gtkmano/Gemfile
@@ -3,7 +3,7 @@ source 'https://rubygems.org'
 gem 'rake', '11.2.2'
 gem 'sinatra', '1.4.7', require: 'sinatra/base'
 gem 'sinatra-contrib', '1.4.7', require: false
-gem 'puma', '3.11.0'
+gem 'puma', '4.3.9'
 gem 'rest-client', '2.0.0'
 gem 'rack-parser', '0.7.0', require: 'rack/parser'
 gem 'sinatra-cross_origin', '0.3.2'
diff --git a/son-gtkmano/Gemfile.lock b/son-gtkmano/Gemfile.lock
index 1e8397dc..b49148af 100644
--- a/son-gtkmano/Gemfile.lock
+++ b/son-gtkmano/Gemfile.lock
@@ -48,11 +48,13 @@ GEM
     minitest (5.11.3)
     multi_json (1.13.1)
     netrc (0.11.0)
+    nio4r (2.5.8)
     parser (2.6.3.0)
       ast (~> 2.4.0)
     pg (0.18.4)
     powerpack (0.1.2)
-    puma (3.11.0)
+    puma (4.3.9)
+      nio4r (~> 2.0)
     rack (1.6.11)
     rack-parser (0.7.0)
       rack
@@ -138,7 +140,7 @@ DEPENDENCIES
   bunny (= 2.5.1)
   ci_reporter_rspec (= 1.0.0)
   pg (= 0.18.4)
-  puma (= 3.11.0)
+  puma (= 4.3.9)
   rack-parser (= 0.7.0)
   rack-test (= 0.6.3)
   rake (= 11.2.2)