diff --git a/.github/workflows/node.yml b/.github/workflows/node.yml
index 747dee243..465729713 100644
--- a/.github/workflows/node.yml
+++ b/.github/workflows/node.yml
@@ -20,3 +20,4 @@ jobs:
           node-version: ${{ matrix.node }}
       - run: npm install
       - run: npm test
+      - run: npm run test:tsd
diff --git a/packages/modeling/src/curves/bezier/arcLengthToT.d.ts b/packages/modeling/src/curves/bezier/arcLengthToT.d.ts
index 225df5a2f..a5294f61b 100644
--- a/packages/modeling/src/curves/bezier/arcLengthToT.d.ts
+++ b/packages/modeling/src/curves/bezier/arcLengthToT.d.ts
@@ -7,4 +7,4 @@ export interface ArcLengthToTOptions {
   segments?: Number
 }
 
-declare function arcLengthToT(options?: ArcLengthToTOptions, bezier: Bezier): number
\ No newline at end of file
+declare function arcLengthToT(options: ArcLengthToTOptions, bezier: Bezier): number