diff --git a/test/user-invocation-table.test.js b/test/user-invocation-table.test.js
index 50cbdc1..bcaea0c 100644
--- a/test/user-invocation-table.test.js
+++ b/test/user-invocation-table.test.js
@@ -75,6 +75,23 @@ describe('concept', () => {
     expr = "next.concept().select($this | $this.next.concept()).display";
     retrieved = fhirpath.evaluate(concepts.a, expr, null, null, options);
     expect(retrieved).toEqual(["B", "C"]);
+  });
+});
+
+describe("toString", () => {
+  it("Works when userInvocationTable passed without overriding toString", () => {
+    const options = {
+      userInvocationTable: {},
+    };
+
+    let result = fhirpath.evaluate(
+      { index: 0 },
+      "index.toString()",
+      null,
+      null,
+      options
+    );
 
+    expect(result).toEqual(["0"]);
   });
 });