VBA To Copy To Last Row For Single Row

I have a macro that determines the last populated row in a region and fills down the formula to the last row. It works awesomely unless there is only ONE row populated, in which case it copies down the row above. Here is the code:

Sub CopyDown()

Dim LastRow As Long
LastRow = Cells(Cells.Rows.Count, "C").End(xlUp).Row
Range("O14").Select
ActiveCell.FormulaR1C1 = "=VLOOKUP(RC[-1],Key!C[-4]:C[-3],2,FALSE)"
Range("O14").Select
Range("O14:O" & LastRow).FillDown
End Sub

I have this code for multiple columns, etc, but they're all using the same "fill down" information.

I'm one of those "create a macro by recording it, then edit it".