diff --git a/src/primitive.test.ts b/src/primitive.test.ts
index c222fe2..b9d10ae 100644
--- a/src/primitive.test.ts
+++ b/src/primitive.test.ts
@@ -307,6 +307,8 @@ test("getMatcher factory rejects patterns outside its contract", () => {
     });
     // @ts-expect-error a gap without a `_` fallback is not exhaustive
     factory({ a: () => 1 });
+    // @ts-expect-error a `string` fallback does not fit the `number` handler
+    factory({ a: () => 1 }, () => "x");
 });
 
 test("getMatcherW factory rejects patterns outside its contract", () => {