workflow fires two times even if i do not change field value in CRM 2011

workflow fires two times even if i do not change field value in CRM 2011

i have workflow in MS CRM 2011 where it fires on certain field change,
when this workflow fires on field change it will first check the boolean
value of flag if the value is yes then set it to no otherwise if flag
value is no then create another "XYZ" entity. but here my problem is when
I change flag value to no it again fires and create another entity "XYZ".