diff --git a/mercurial/bundlerepo.py b/mercurial/bundlerepo.py
--- a/mercurial/bundlerepo.py
+++ b/mercurial/bundlerepo.py
@@ -264,24 +264,6 @@
 
 class bundlerepository(localrepo.localrepository):
     def __init__(self, ui, path, bundlename):
-        def _writetempbundle(read, suffix, header=''):
-            """Write a temporary file to disk
-
-            This is closure because we need to make sure this tracked by
-            self.tempfile for cleanup purposes."""
-            fdtemp, temp = self.vfs.mkstemp(prefix="hg-bundle-",
-                                            suffix=".hg10un")
-            self.tempfile = temp
-
-            with os.fdopen(fdtemp, pycompat.sysstr('wb')) as fptemp:
-                fptemp.write(header)
-                while True:
-                    chunk = read(2**18)
-                    if not chunk:
-                        break
-                    fptemp.write(chunk)
-
-            return self.vfs.open(self.tempfile, mode="rb")
         self._tempparent = None
         try:
             localrepo.localrepository.__init__(self, ui, path)
@@ -314,8 +296,8 @@
                         msg = _('Unsupported changegroup version: %s')
                         raise error.Abort(msg % version)
                     if self.bundle.compressed():
-                        cgstream = _writetempbundle(part.read,
-                                                    ".cg%sun" % version)
+                        cgstream = self._writetempbundle(part.read,
+                                                         ".cg%sun" % version)
 
             if cgstream is None:
                 raise error.Abort(_('No changegroups found'))
@@ -324,7 +306,8 @@
             self.bundle = changegroup.getunbundler(version, cgstream, 'UN')
 
         elif self.bundle.compressed():
-            f = _writetempbundle(self.bundle.read, '.hg10un', header='HG10UN')
+            f = self._writetempbundle(self.bundle.read, '.hg10un',
+                                      header='HG10UN')
             self.bundlefile = self.bundle = exchange.readbundle(ui, f,
                                                                 bundlename,
                                                                 self.vfs)
@@ -336,6 +319,23 @@
         phases.retractboundary(self, None, phases.draft,
                                [ctx.node() for ctx in self[self.firstnewrev:]])
 
+    def _writetempbundle(self, readfn, suffix, header=''):
+        """Write a temporary file to disk
+        """
+        fdtemp, temp = self.vfs.mkstemp(prefix="hg-bundle-",
+                                        suffix=".hg10un")
+        self.tempfile = temp
+
+        with os.fdopen(fdtemp, pycompat.sysstr('wb')) as fptemp:
+            fptemp.write(header)
+            while True:
+                chunk = readfn(2**18)
+                if not chunk:
+                    break
+                fptemp.write(chunk)
+
+        return self.vfs.open(self.tempfile, mode="rb")
+
     @localrepo.unfilteredpropertycache
     def _phasecache(self):
         return bundlephasecache(self, self._phasedefaults)