diff --git a/src/curve.d.ts b/src/curve.d.ts
index 69acaf77b3..cf031a24b5 100644
--- a/src/curve.d.ts
+++ b/src/curve.d.ts
@@ -97,7 +97,7 @@ export interface CurveAutoOptions {
    *
    * [1]: https://d3js.org/d3-shape/curve#custom-curves
    */
-  curve?: Curve | "auto";
+  curve?: Curve | "auto" | undefined;
 
   /**
    * The tension option only has an effect on bundle, cardinal and Catmull–Rom
diff --git a/src/mark.d.ts b/src/mark.d.ts
index 54f14276ca..70174fee36 100644
--- a/src/mark.d.ts
+++ b/src/mark.d.ts
@@ -403,7 +403,7 @@ export interface MarkOptions {
    *
    * [1]: https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/opacity
    */
-  opacity?: ChannelValueSpec;
+  opacity?: ChannelValueSpec | undefined;
 
   /**
    * The [mix-blend-mode][1]; a constant string specifying how to blend content