diff --git a/Lib/tarfile.py b/Lib/tarfile.py
index ef316b5..125d95d 100644
--- a/Lib/tarfile.py
+++ b/Lib/tarfile.py
@@ -349,7 +349,7 @@
         }[mode]
         if hasattr(os, "O_BINARY"):
             mode |= os.O_BINARY
-        self.fd = os.open(name, mode)
+        self.fd = os.open(name, mode, 0o666)
 
     def close(self):
         os.close(self.fd)