Index: lib/redmine/nested_set/issue_nested_set.rb
===================================================================
--- lib/redmine/nested_set/issue_nested_set.rb	(revision 14100)
+++ lib/redmine/nested_set/issue_nested_set.rb	(working copy)
@@ -149,16 +149,20 @@
       end
 
       def lock_nested_set
-        if self.class.connection.adapter_name =~ /sqlserver/i
-          lock = "WITH (ROWLOCK HOLDLOCK UPDLOCK)"
-          # Custom lock for SQLServer
+        if Redmine::Database.postgresql?
+          sets_to_lock = [id, parent_id].compact
+          self.class.reorder(:id).where("root_id IN (SELECT root_id FROM #{self.class.table_name} WHERE id IN (?))", sets_to_lock).lock.ids
+        else
+          lock = true
           # This can be problematic if root_id or parent root_id changes
           # before locking
           sets_to_lock = [root_id, parent.try(:root_id)].compact.uniq
-          self.class.reorder(:id).where(:root_id => sets_to_lock).lock(lock).ids
-        else
-          sets_to_lock = [id, parent_id].compact
-          self.class.reorder(:id).where("root_id IN (SELECT root_id FROM #{self.class.table_name} WHERE id IN (?))", sets_to_lock).lock.ids
+          if self.class.connection.adapter_name =~ /sqlserver/i
+            # Custom lock for SQLServer
+            lock = "WITH (ROWLOCK HOLDLOCK UPDLOCK)"
+          end
+          # No need to instanciate records
+          self.class.connection.execute(self.class.reorder(:id).where(:root_id => sets_to_lock).lock.to_sql)
         end
       end