diff --git a/packages/tools/src/vercel/index.ts b/packages/tools/src/vercel/index.ts
index 54bc5dcf..e87f31b6 100644
--- a/packages/tools/src/vercel/index.ts
+++ b/packages/tools/src/vercel/index.ts
@@ -216,7 +216,12 @@ const wrapVercelLanguageModel = <T extends LanguageModel>(
 
 	const wrappedModel = new Proxy(model, {
 		get(target, prop, _receiver) {
-			if (typeof prop === "string" && prop in overrides) {
+			// Use hasOwnProperty to avoid matching inherited Object.prototype props
+			// (e.g. 'constructor', 'toString') which would shadow them on the proxy.
+			if (
+				typeof prop === "string" &&
+				Object.prototype.hasOwnProperty.call(overrides, prop)
+			) {
 				return overrides[prop]
 			}
 			// Delegate to the original model so that `this` inside prototype
diff --git a/packages/tools/test/with-supermemory/unit.test.ts b/packages/tools/test/with-supermemory/unit.test.ts
index 4a7695f4..f625a95b 100644
--- a/packages/tools/test/with-supermemory/unit.test.ts
+++ b/packages/tools/test/with-supermemory/unit.test.ts
@@ -216,6 +216,24 @@ describe("Unit: withSupermemory", () => {
 		})
 	})
 
+	describe("Proxy override correctness", () => {
+		it("should not shadow Object.prototype inherited props (e.g. constructor) with undefined overrides", () => {
+			process.env.SUPERMEMORY_API_KEY = "test-key"
+
+			// 'constructor', 'toString', 'hasOwnProperty' etc are in Object.prototype.
+			// Using `prop in overrides` (instead of hasOwnProperty) would match these
+			// inherited props and return undefined from the overrides map, shadowing
+			// the real implementations on the model/target.
+			const mockModel = createMockV3LanguageModel()
+			const wrappedModel = withSupermemory(mockModel, TEST_CONFIG.containerTag)
+
+			// constructor should point to the model's class, not Object
+			expect((wrappedModel as object).constructor).toBe(MockLanguageModelV3)
+			// toString should be callable and not undefined
+			expect(typeof (wrappedModel as object).toString).toBe("function")
+		})
+	})
+
 	describe("Memory caching", () => {
 		let fetchMock: ReturnType<typeof vi.fn>