How to get the correct count records instead of counting the field name twice?

[ksbuchanan]

Here is my search:

source="WinEventLog:Security" EventCode="4723" OR EventCode="529" | eval UserName=coalesce(User_Name,Account_Name) | stats count by UserName |sort -count |head 10

The problem is that the field "Account_Name" appears more than once in the record, so the count is effectively doubled. How can I get the correct count of the records instead of counting the field name twice?