diff --git a/bezier-js/index.d.ts b/bezier-js/index.d.ts
index ff07e67f16..7706a46472 100644
--- a/bezier-js/index.d.ts
+++ b/bezier-js/index.d.ts
@@ -51,6 +51,7 @@ declare namespace BezierJs {
         e: number;
         r: number;
         s: number;
+        interval: { start: number; end: number; };
     }
     interface Shape {
         startcap: BezierCap;