pt-table-sync with no unique index - fails with no more space left


I have a master-slave replication and I’m having trouble syncing one table that has no unique index, so I used the --no-check-slave option and when I thought it all goes well, error occurred:
Error writing file ‘/dev/shm/MYGFvDuG’ (Errcode: 28) [for Statement “SELECT [B]column1[/B], [B]column2[/B], [B]column3[/B], COUNT(*) AS __maatkit_count FROM [B]database[/B].[B]table[/B] WHERE 1=1 GROUP BY [B]column1[/B], [B]column2[/B], [B]column3[/B] ORDER BY [B]column1[/B], [B]column2[/B], [B]column3[/B] LOCK IN SHARE MODE”] at line 5301 while doing database.table on slave.server

The command I used is:
pt-table-sync --execute --no-check-slave h=localhost,D=database,t=table h=slave.server,u=user,p=password,D=database,t=table

The dry-run looks ok, no errors, version: pt-table-sync 2.1.1

I know the problem is that the query quickly eats all the ram, then goes writing in /dev/shm/ until it fills it, then fails with no more space left…
Mysql error log shows: [ERROR] /usr/sbin/mysqld: Sort aborted

Any solution to write it somewhere else? Or any other solution?

Any help will be really appreciated.