diff --git a/src/authm_mad/remotes/ldap/ldap_auth.rb b/src/authm_mad/remotes/ldap/ldap_auth.rb
index 7f5bbbd3f0..359425f487 100644
--- a/src/authm_mad/remotes/ldap/ldap_auth.rb
+++ b/src/authm_mad/remotes/ldap/ldap_auth.rb
@@ -161,7 +161,8 @@ class OpenNebula::LdapAuth
     end
 
     def is_in_group?(user, group)
-        username = user.first.force_encoding(Encoding::UTF_8)
+        username = Net::LDAP::Filter.escape(
+            user.first.force_encoding(Encoding::UTF_8))
         result=@ldap.search(
                     :base   => group,
                     :attributes => [@options[:group_field]],