Month Name column sorting help

[mrchonginhk]

I have created a date table and have marked it as date table in Power BI

Apart from date, there is a Month Name column I have created like Jul-18 etc
When I use this MonthName dimension in visuals like Matrix,
Apr become first as it starts with an "A"

So how can we ensure it is ordered by date instead of ordered by name ?
I tried click the MonthName field and then select Sort By Another Column then select Date but it returns an error:
"We can't sort this column by 'Date'. There can't be more than one value in 'Date' for the same value in 'MonthName' "

What can we do ?
Thanks

 

[SpillerBD]

In the Power Pivot Window, use the "Sort by Column" to associate the order with the Month Number.