diff --git a/CHANGELOG.md b/CHANGELOG.md
index ee8c7bd..bbc1649 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,10 @@
 This log documents significant changes for each release.  This project follows
 [Semantic Versioning](http://semver.org/).
 
+## [3.16.2] - 2025-01-16
+### Fixed
+- Bug with toString when userInvocationTable passed.
+
 ## [3.16.1] - 2025-01-09
 ### Fixed
 - Read environment variables only when they are used in an expression, avoiding
diff --git a/package-lock.json b/package-lock.json
index c7c6959..766823c 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "fhirpath",
-  "version": "3.16.1",
+  "version": "3.16.2",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "fhirpath",
-      "version": "3.16.1",
+      "version": "3.16.2",
       "hasInstallScript": true,
       "license": "SEE LICENSE in LICENSE.md",
       "dependencies": {
diff --git a/package.json b/package.json
index 5e77dbd..f7d462e 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "fhirpath",
-  "version": "3.16.1",
+  "version": "3.16.2",
   "description": "A FHIRPath engine",
   "main": "src/fhirpath.js",
   "types": "src/fhirpath.d.ts",
diff --git a/src/fhirpath.js b/src/fhirpath.js
index 8b7fafc..66fba29 100644
--- a/src/fhirpath.js
+++ b/src/fhirpath.js
@@ -506,7 +506,10 @@ function makeParam(ctx, parentData, type, param) {
 }
 
 function doInvoke(ctx, fnName, data, rawParams){
-  var invoc = ctx.userInvocationTable?.[fnName]
+  var invoc =
+    ctx.userInvocationTable
+    && Object.prototype.hasOwnProperty.call(ctx.userInvocationTable, fnName)
+    && ctx.userInvocationTable?.[fnName]
     || engine.invocationTable[fnName]
     || data.length === 1 && data[0]?.invocationTable[fnName];
   var res;
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"]);
   });
 });