diff --git a/lib/index.d.ts b/lib/index.d.ts
index ecd1cf834..f65c813d5 100644
--- a/lib/index.d.ts
+++ b/lib/index.d.ts
@@ -1341,7 +1341,7 @@ declare namespace sharp {
         /** A value between 0.3 and 1000 representing the sigma of the Gaussian mask, where `sigma = 1 + radius / 2` */
         sigma: number;
         /** How accurate the operation should be, one of: integer, float, approximate. (optional, default "integer") */
-        precision: Precision | undefined;
+        precision?: Precision | undefined;
     }
 
     interface FlattenOptions {