diff --git a/lib/full_url_for.ts b/lib/full_url_for.ts
index 6c5e4e9..cb55c53 100644
--- a/lib/full_url_for.ts
+++ b/lib/full_url_for.ts
@@ -2,9 +2,9 @@ import { parse } from 'url';
 import encodeURL from './encode_url';
 import prettyUrls from './pretty_urls';
 import Cache from './cache';
-const cache = new Cache();
+const cache = new Cache<string>();
 
-function fullUrlForHelper(path = '/'): string {
+function fullUrlForHelper(path = '/') {
   const { config } = this;
   const prettyUrlsOptions = Object.assign({
     trailing_index: true,
@@ -25,7 +25,7 @@ function fullUrlForHelper(path = '/'): string {
     path = prettyUrls(path, prettyUrlsOptions);
 
     return path;
-  }) as string;
+  });
 }
 
 export = fullUrlForHelper;