shrinking a partitionned table

 Hello , I am trying to shrink a partitioned table :

alter table myOwner.myTable enable row movement;
is ok

alter table myOwner.myTable modify partition myPartition shrink space;
give this error :
Erreur SQL : ORA-10631: SHRINK clause should not be specified for this object
10631. 00000 -  "SHRINK clause should not be specified for this object"
*Cause:    It is incorrect to issue shrink on the object
*Action:   Verify the object name and type and reissue the command

i do not see what's wrong...

thanks