diff --git a/engines/plos_authors/Gemfile.lock b/engines/plos_authors/Gemfile.lock
index db40dcb53..4229b3741 100644
--- a/engines/plos_authors/Gemfile.lock
+++ b/engines/plos_authors/Gemfile.lock
@@ -35,9 +35,11 @@ GEM
       tzinfo (~> 1.1)
     arel (5.0.1.20140414130214)
     builder (3.2.2)
+    concurrent-ruby (1.1.10)
     erubis (2.7.0)
     hike (1.2.3)
-    i18n (0.6.11)
+    i18n (0.9.5)
+      concurrent-ruby (~> 1.0)
     json (1.8.1)
     mail (2.6.1)
       mime-types (>= 1.16, < 3)