diff --git a/src/ratelimit.ts b/src/ratelimit.ts
index 38cfaae..0c669cc 100644
--- a/src/ratelimit.ts
+++ b/src/ratelimit.ts
@@ -405,6 +405,6 @@ export abstract class Ratelimit<TContext extends Context> {
     req?: Pick<LimitOptions, "ip" | "userAgent" | "country">
   ): string[] => {
     const members = [identifier, req?.ip, req?.userAgent, req?.country];
-    return members.filter(Boolean)
+    return members.filter((item): item is string => Boolean(item));
   }
 }
diff --git a/src/single.ts b/src/single.ts
index 3703da1..a9dd352 100644
--- a/src/single.ts
+++ b/src/single.ts
@@ -2,6 +2,7 @@ import type { Duration } from "./duration";
 import { ms } from "./duration";
 import { safeEval } from "./hash";
 import { RESET_SCRIPT, SCRIPTS } from "./lua-scripts/hash";
+import { tokenBucketIdentifierNotFound } from "./lua-scripts/single";
 
 import { Ratelimit } from "./ratelimit";
 import type { Algorithm, RegionContext } from "./types";