Sub Test()
    Dim x As Long
    Dim y As Long

    x = 65536   ' 64K <-- Ok

    x = 64
    x = x * 1024    ' 64K <-- Ok
    
    y = 64
    x = y * 1024    ' 64K <-- Ok

    x = 64 * 1024   ' 64K <-- Run-time error '6': Overflow
    x = CLng(64 * 1024)   ' 64K <-- Run-time error '6': Overflow
End Sub