diff --git a/src/wormhole/cli/cmd_receive.py b/src/wormhole/cli/cmd_receive.py
index 7725305..79a6221 100644
--- a/src/wormhole/cli/cmd_receive.py
+++ b/src/wormhole/cli/cmd_receive.py
@@ -284,29 +284,30 @@ class TwistedReceiver:
         self._msg(u"Received file written to %s" %
                   os.path.basename(self.abs_destname))
 
+    def _extract_file(self, zf, info, extract_dir):
+        """
+        the zipfile module does not restore file permissions
+        so we'll do it manually
+        """
+        out_path = os.path.join( extract_dir, info.filename )
+        out_path = os.path.abspath( out_path )
+        if not out_path.startswith( extract_dir ):
+            raise ValueError( "malicious zipfile, %s outside of extract_dir %s"
+                    % (info.filename, extract_dir) )
+
+        zf.extract( info.filename, path=extract_dir )
+
+        # not sure why zipfiles store the perms 16 bits away but they do
+        perm = info.external_attr >> 16
+        os.chmod( out_path, perm )
+
     def _write_directory(self, f):
-        def extract_file( zf, info, extract_dir ):
-            """
-            the zipfile module does not restore file permissions
-            so we'll do it manually
-            """
-            out_path = os.path.join( extract_dir, info.filename )
-            out_path = os.path.abspath( out_path )
-            if not out_path.startswith( extract_dir ):
-                raise ValueError( "malicious zipfile, %s outside of extract_dir %s"
-                        % (info.filename, extract_dir) )
-
-            zf.extract( info.filename, path=extract_dir )
-
-            # not sure why zipfiles store the perms 16 bits away but they do
-            perm = info.external_attr >> 16
-            os.chmod( out_path, perm )
 
         self._msg(u"Unpacking zipfile..")
         with self.args.timing.add("unpack zip"):
             with zipfile.ZipFile(f, "r", zipfile.ZIP_DEFLATED) as zf:
                 for info in zf.infolist():
-                    extract_file( zf, info, self.abs_destname )
+                    self._extract_file( zf, info, self.abs_destname )
 
             self._msg(u"Received files written to %s/" %
                       os.path.basename(self.abs_destname))
diff --git a/src/wormhole/test/test_scripts.py b/src/wormhole/test/test_scripts.py
index 5bf89be..6ccd5f1 100644
--- a/src/wormhole/test/test_scripts.py
+++ b/src/wormhole/test/test_scripts.py
@@ -1,5 +1,6 @@
 from __future__ import print_function
 import os, sys, re, io, zipfile, six
+import mock
 from twisted.trial import unittest
 from twisted.python import procutils, log
 from twisted.internet.utils import getProcessOutputAndValue
@@ -613,3 +614,44 @@ class Cleanup(ServerBase, unittest.TestCase):
         self.assertEqual(len(cids), 0)
         self.flushLoggedErrors(WrongPasswordError)
 
+class ExtractFile(unittest.TestCase):
+    def test_filenames(self):
+        args = mock.Mock()
+        args.relay_url = u""
+        ef = cmd_receive.TwistedReceiver(args)._extract_file
+        extract_dir = os.path.abspath(self.mktemp())
+
+        zf = mock.Mock()
+        zi = mock.Mock()
+        zi.filename = "ok"
+        zi.external_attr = 5 << 16
+        expected = os.path.join(extract_dir, "ok")
+        with mock.patch.object(cmd_receive.os, "chmod") as chmod:
+            ef(zf, zi, extract_dir)
+            self.assertEqual(zf.extract.mock_calls,
+                             [mock.call(zi.filename, path=extract_dir)])
+            self.assertEqual(chmod.mock_calls, [mock.call(expected, 5)])
+
+        zf = mock.Mock()
+        zi = mock.Mock()
+        zi.filename = "../haha"
+        e = self.assertRaises(ValueError, ef, zf, zi, extract_dir)
+        self.assertIn("malicious zipfile", str(e))
+
+        zf = mock.Mock()
+        zi = mock.Mock()
+        zi.filename = "haha//root" # abspath squashes this, hopefully zipfile
+                                   # does too
+        zi.external_attr = 5 << 16
+        expected = os.path.join(extract_dir, "haha/root")
+        with mock.patch.object(cmd_receive.os, "chmod") as chmod:
+            ef(zf, zi, extract_dir)
+            self.assertEqual(zf.extract.mock_calls,
+                             [mock.call(zi.filename, path=extract_dir)])
+            self.assertEqual(chmod.mock_calls, [mock.call(expected, 5)])
+
+        zf = mock.Mock()
+        zi = mock.Mock()
+        zi.filename = "/etc/passwd"
+        e = self.assertRaises(ValueError, ef, zf, zi, extract_dir)
+        self.assertIn("malicious zipfile", str(e))