Empty Range Bound Specified for Partition

pgsql> create table test_parent_partition(

item_id integer,

         item_name character varying,

         item_qty character varying)

             partition by range(item_qty);

pgsql>  create table test_upto_50 partition of test_parent_partition

              for values from ('0') to ('50');

Above 1st partition table was created. After that i have taken next step to create another partition talbe. But while am creating another partition table like below query. 

pgsql>  create table test_upto_100 partition of test_parent_partition

             for values from ('51') to ('100');

               It was showing error like this..

ERROR: empty range bound specified for partition "test_upto_100" DETAIL: Specified lower bound ('51') is greater than or equal to upper bound ('100'). SQL state: 42P17 

            

                I am not getting, please give me cause of this and solution.