diff --git a/src/im_mad/remotes/lib/vcenter_cluster.rb b/src/im_mad/remotes/lib/vcenter_cluster.rb
index f9835b2937..b268e4bc33 100644
--- a/src/im_mad/remotes/lib/vcenter_cluster.rb
+++ b/src/im_mad/remotes/lib/vcenter_cluster.rb
@@ -738,6 +738,8 @@ class ClusterSet
 
     # Add a host by id, it access OpenNebula to get connection parameters
     def add(hid, conf)
+        return if @mutex.synchronize { @clusters.key?(hid) }
+
         begin
             cluster = Cluster.new(hid, @client)
             error   = ''