diff --git a/slist/__init__.py b/slist/__init__.py
index ca8afa0..faf6264 100644
--- a/slist/__init__.py
+++ b/slist/__init__.py
@@ -576,7 +576,7 @@ def matches_search(text: str) -> bool:
 
         return self.filter(predicate=lambda item: matches_search(key(item)))
 
-    def mk_string(self: Slist[str], sep: str) -> str:
+    def mk_string(self: Sequence[str], sep: str) -> str:
         return sep.join(self)
 
     @overload