diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index 4c7dadb..261d9fb 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -1842,7 +1842,7 @@
             tarinfo.type = DIRTYPE
 
         # Directory names should have a '/' at the end.
-        if tarinfo.isdir():
+        if tarinfo.isdir() and not tarinfo.name.endswith("/"):
             tarinfo.name += "/"
 
         self.members.append(tarinfo)