diff --git a/Gemfile.lock b/Gemfile.lock
index 996fc318..ee509276 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -730,6 +730,7 @@ GEM
     multi_json (1.13.1)
     multipart-post (2.0.0)
     mustermann (1.0.3)
+    nio4r (2.5.8)
     opencensus (0.4.0)
     opencensus-stackdriver (0.2.0)
       concurrent-ruby (~> 1.0)
@@ -746,7 +747,8 @@ GEM
       coderay (~> 1.1.0)
       method_source (~> 0.9.0)
     public_suffix (3.0.3)
-    puma (3.12.6)
+    puma (4.3.11)
+      nio4r (~> 2.0)
     pusher (1.3.2)
       httpclient (~> 2.7)
       multi_json (~> 1.0)