diff --git a/stdlib/2and3/tarfile.pyi b/stdlib/2and3/tarfile.pyi
index 4262fedc9..366dfb1f6 100644
--- a/stdlib/2and3/tarfile.pyi
+++ b/stdlib/2and3/tarfile.pyi
@@ -101,7 +101,7 @@ class TarFile(Iterable[TarInfo]):
         pax_headers: Optional[Mapping[str, str]] = ...,
         debug: Optional[int] = ...,
         errorlevel: Optional[int] = ...,
-        compresslevel: Optional[int] = ...,
+        copybufsize: Optional[int] = ...,  # undocumented
     ) -> None: ...
     def __enter__(self) -> TarFile: ...
     def __exit__(
diff --git a/tests/stubtest_whitelists/py35.txt b/tests/stubtest_whitelists/py35.txt
index 366f5b9f0..6aff3d68a 100644
--- a/tests/stubtest_whitelists/py35.txt
+++ b/tests/stubtest_whitelists/py35.txt
@@ -48,6 +48,7 @@ smtpd.SMTPChannel.__init__
 smtpd.SMTPServer.__init__
 sre_compile.dis
 ssl.SSLSocket.__init__
+tarfile.TarFile.__init__  # undocumented arg copybufsize doesn't exist
 typing.Coroutine.cr_await
 typing.Coroutine.cr_code
 typing.Coroutine.cr_frame
diff --git a/tests/stubtest_whitelists/py3_common.txt b/tests/stubtest_whitelists/py3_common.txt
index dc2240790..2a7a9004a 100644
--- a/tests/stubtest_whitelists/py3_common.txt
+++ b/tests/stubtest_whitelists/py3_common.txt
@@ -377,9 +377,7 @@ sys.gettotalrefcount
 sys.implementation
 sysconfig.is_python_build
 sysconfig.parse_config_h
-tarfile.TarFile.__init__
 tarfile.TarFile.errors
-tarfile.TarFile.tarinfo
 tempfile.SpooledTemporaryFile.__next__
 tempfile.SpooledTemporaryFile.readable
 tempfile.SpooledTemporaryFile.seekable