diff --git a/index.d.ts b/index.d.ts
index d42fb1d..5594ea1 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -17,6 +17,12 @@ declare namespace stableStringify {
     };
 }
 
+declare function stableStringify(
+    obj: string | number | boolean | Record<keyof any, unknown> | unknown[] | null
+): string;
+declare function stableStringify(
+    obj: undefined
+): undefined;
 declare function stableStringify(
     obj: unknown,
     options?: (stableStringify.Comparator & stableStringify.StableStringifyOptions) | stableStringify.StableStringifyOptions,