diff --git a/types/fetch-mock/index.d.ts b/types/fetch-mock/index.d.ts
index 8c441ea26a..a8df26e43a 100644
--- a/types/fetch-mock/index.d.ts
+++ b/types/fetch-mock/index.d.ts
@@ -82,7 +82,7 @@ declare namespace fetchMock {
         /**
          * Set the response headers.
          */
-        headers?: { [key: string]: string | number };
+        headers?: { [key: string]: string };
 
         /**
          * If this property is present then a Promise rejected with the value