diff --git a/typescript/src/ts/program.ts b/typescript/src/ts/program.ts
index b771c653..149e69a5 100644
--- a/typescript/src/ts/program.ts
+++ b/typescript/src/ts/program.ts
@@ -99,7 +99,7 @@ function isValidFunctionName(name: unknown): name is string {
 export function createModuleTextFromProgram(jsonObject: object): Result<string> {
     const steps = (jsonObject as Program)["@steps"];
     if (!(Array.isArray(steps) && steps.every(step => typeof step === "object" && step !== null && Object.prototype.hasOwnProperty.call(step, "@func")))) {
-        return error("JSON object is not a valid program", { data: jsonObject });
+        return error("JSON object is not a valid program", { data: jsonObject });
     }
     let hasError = false;
     let functionBody = "";
@@ -109,7 +109,7 @@ export function createModuleTextFromProgram(jsonObject: object): Result<string>
         currentStep++;
     }
     return hasError ?
-        error("JSON program contains an invalid expression", { data: jsonObject }) :
+        error("JSON program contains an invalid expression", { data: jsonObject }) :
         success(`import { API } from "./schema";\nfunction program(api: API) {\n${functionBody}}`);
 
     function exprToString(expr: unknown): string {
@@ -137,7 +137,7 @@ export function createModuleTextFromProgram(jsonObject: object): Result<string>
             return `[${arrayToString(obj)}]`;
         }
         else {
-            return `{ ${Object.keys(obj).map(key => `${JSON.stringify(key)}: ${exprToString(obj[key])}`).join(", ")} }`;
+            return `{ ${Object.keys(obj).map(key => `${key === "__proto__" ? `["__proto__"]` : JSON.stringify(key)}: ${exprToString(obj[key])}`).join(", ")} }`;
         }
         hasError = true;
         return "";
@@ -213,11 +213,11 @@ export async function evaluateJsonProgram(program: Program, onCall: (func: strin
  * @returns A `TypeChatJsonTranslator<Program>` instance.
  */
 export function createProgramTranslator(model: TypeChatLanguageModel, schema: string): TypeChatJsonTranslator<Program> {
-    const validator = createTypeScriptJsonValidator<Program>(
-        schema,
-        "Program",
-        "API"
-    );
+    const validator = createTypeScriptJsonValidator<Program>(
+        schema,
+        "Program",
+        "API"
+    );
     validator.createModuleTextFromJson = createModuleTextFromProgram;
     const translator = createJsonTranslator<Program>(model, validator);
     translator.createRequestPrompt = createRequestPrompt;
diff --git a/typescript/test/program.test.ts b/typescript/test/program.test.ts
index 5eaa8183..f7cdbd1c 100644
--- a/typescript/test/program.test.ts
+++ b/typescript/test/program.test.ts
@@ -186,6 +186,37 @@ describe("hasOwnProperty shadowing in parsed programs", () => {
     });
 });
 
+describe("__proto__ as object property key", () => {
+    it("generates a computed property name for a string value", () => {
+        const program = JSON.parse('{"@steps":[{"@func":"first","@args":[{"__proto__":"hello"}]}]}');
+        const result = createModuleTextFromProgram(program);
+        assert.equal(result.success, true);
+        assert.match((result as { data: string }).data, /\["__proto__"\]: "hello"/);
+        assert.doesNotMatch((result as { data: string }).data, /"__proto__": "hello"/);
+    });
+
+    it("generates a computed property name for a numeric value", () => {
+        const program = JSON.parse('{"@steps":[{"@func":"first","@args":[{"__proto__":42}]}]}');
+        const result = createModuleTextFromProgram(program);
+        assert.equal(result.success, true);
+        assert.match((result as { data: string }).data, /\["__proto__"\]: 42/);
+    });
+
+    it("generates a computed property name for a null value", () => {
+        const program = JSON.parse('{"@steps":[{"@func":"first","@args":[{"__proto__":null}]}]}');
+        const result = createModuleTextFromProgram(program);
+        assert.equal(result.success, true);
+        assert.match((result as { data: string }).data, /\["__proto__"\]: null/);
+    });
+
+    it("evaluates an object with __proto__ as an own data property", async () => {
+        const program = JSON.parse('{"@steps":[{"@func":"first","@args":[{"__proto__":"value"}]}]}');
+        const result = await evaluateJsonProgram(program, async (_func, args) => args[0]);
+        assert.ok(Object.prototype.hasOwnProperty.call(result, "__proto__"));
+        assert.equal((result as Record<string, unknown>)["__proto__"], "value");
+    });
+});
+
 describe("@func name validation", () => {
     const maliciousProgram: Program = {
         "@steps": [