diff --git a/s3fs/core.py b/s3fs/core.py
index 6b80ad89..3d03396a 100644
--- a/s3fs/core.py
+++ b/s3fs/core.py
@@ -746,7 +746,7 @@ async def _lsdir(
         if not prefix:
             prefix = ""
         if key:
-            prefix = key.lstrip("/") + "/" + prefix
+            prefix = key + "/" + prefix
         if path not in self.dircache or refresh or not delimiter or versions:
             try:
                 logger.debug("Get directory listing page for %s" % path)