diff --git a/Gemfile.lock b/Gemfile.lock
index 57d4c2c..6380b97 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -90,6 +90,7 @@ GEM
     mustermann (1.0.3)
     net-http-persistent (3.0.0)
       connection_pool (~> 2.2)
+    nio4r (2.5.8)
     nokogiri (1.10.4)
       mini_portile2 (~> 2.4.0)
     parslet (1.8.1)
@@ -98,7 +99,8 @@ GEM
       cliver (~> 0.3.1)
       websocket-driver (>= 0.2.0)
     public_suffix (3.0.0)
-    puma (3.10.0)
+    puma (4.3.12)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-cache (1.7.1)
       rack (>= 0.4)