diff --git a/lib/docker_manager/upgrader.rb b/lib/docker_manager/upgrader.rb
index 8f4ecab..4eb6b91 100644
--- a/lib/docker_manager/upgrader.rb
+++ b/lib/docker_manager/upgrader.rb
@@ -37,7 +37,7 @@ class DockerManager::Upgrader
 
   def run(cmd)
     log "$ #{cmd}"
-    IO.popen("cd #{Rails.root} && RAILS_ENV=production #{cmd} 2>&1") do |line|
+    IO.popen("cd #{Rails.root} && RUBYOPT= RAILS_ENV=production #{cmd} 2>&1") do |line|
       log(line.read)
     end