diff --git a/Gemfile.lock b/Gemfile.lock
index 0f087bd..7cae9c6 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -15,6 +15,7 @@ GEM
     mini_portile2 (2.4.0)
     multi_json (1.13.1)
     mustermann (1.0.3)
+    nio4r (2.5.8)
     nokogiri (1.10.3)
       mini_portile2 (~> 2.4.0)
     oj (3.7.12)
@@ -26,7 +27,8 @@ GEM
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     public_suffix (3.0.3)
-    puma (3.12.1)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-contrib (2.1.0)
       rack (~> 2.0)