diff --git a/engines/plos_authors/Gemfile.lock b/engines/plos_authors/Gemfile.lock
index db40dcb53..bcc2bee7a 100644
--- a/engines/plos_authors/Gemfile.lock
+++ b/engines/plos_authors/Gemfile.lock
@@ -44,7 +44,7 @@ GEM
     mime-types (2.4.1)
     minitest (5.4.2)
     multi_json (1.10.1)
-    rack (1.5.2)
+    rack (1.5.5)
     rack-test (0.6.2)
       rack (>= 1.0)
     rails (4.1.6)