diff --git a/Gemfile b/Gemfile
index 867bc4a52..f416bc87f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -24,6 +24,7 @@ gem 'redis-rails'
 # background processing
 gem 'sidekiq'
 gem 'sidekiq-unique-jobs'
+gem 'celluloid', '0.16.0' # unpeg when new sidekiq released: https://github.com/mperham/sidekiq/issues/2397
 gem 'whenever', require: false # to manage crontab
 
 # data model
diff --git a/Gemfile.lock b/Gemfile.lock
index 590929423..3a4786c34 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -89,7 +89,7 @@ GEM
     byebug (5.0.0)
       columnize (= 0.9.0)
     c_geohash (1.1.2)
-    celluloid (0.16.1)
+    celluloid (0.16.0)
       timers (~> 4.0.0)
     certifi (2015.08.10)
     choice (0.2.0)
@@ -343,6 +343,7 @@ DEPENDENCIES
   bullet
   byebug
   c_geohash
+  celluloid (= 0.16.0)
   database_cleaner
   datastore_admin!
   enumerize