diff --git a/appengine/flexible/ruby31-and-earlier/static_files/rails/Gemfile.lock b/appengine/flexible/ruby31-and-earlier/static_files/rails/Gemfile.lock
index eb5c0ebdc..5782b3af6 100644
--- a/appengine/flexible/ruby31-and-earlier/static_files/rails/Gemfile.lock
+++ b/appengine/flexible/ruby31-and-earlier/static_files/rails/Gemfile.lock
@@ -60,7 +60,7 @@ GEM
       coffee-script-source
       execjs
     coffee-script-source (1.12.2)
-    concurrent-ruby (1.2.2)
+    concurrent-ruby (1.3.7)
     crass (1.0.6)
     cuprite (0.14.3)
       capybara (~> 3.0)