The sum of the interior angles of a polygon can be calculated using the formula:
\[ \text{Sum of interior angles} = (n - 2) \times 180° \]
where \( n \) is the number of sides of the polygon.
For a nonagon, \( n = 9 \).
Plugging in the values:
\[ \text{Sum of interior angles} = (9 - 2) \times 180° \] \[ = 7 \times 180° \] \[ = 1260° \]
Thus, the sum of the interior angles of a nonagon is 1260°.