diff --git a/src/__tests__/flip.spec.ts b/src/__tests__/flip.spec.ts
index a7ba0167..a4cbe338 100644
--- a/src/__tests__/flip.spec.ts
+++ b/src/__tests__/flip.spec.ts
@@ -63,9 +63,11 @@ describe('flip', () => {
       .toThrow(new TypeError('Expected Object, got string testing'));
     expect(() => flip({}, {
       follow: invalidFollow as boolean,
+      useToString: false,
     }))
       .toThrow(new TypeError('Expected Boolean, got string testing'));
     expect(() => flip({}, {
+      follow: false,
       useToString: invalidUseToString as boolean,
     }))
       .toThrow(new TypeError('Expected Boolean, got string testing'));