diff --git a/_pytest/tmpdir.py b/_pytest/tmpdir.py
index cff39065f..a2a063200 100644
--- a/_pytest/tmpdir.py
+++ b/_pytest/tmpdir.py
@@ -54,13 +54,8 @@ class TempdirFactory:
             else:
                 # use a sub-directory in the temproot to speed-up
                 # make_numbered_dir() call
-                import getpass
                 temproot = py.path.local.get_temproot()
-                try:
-                    rootdir = temproot.join('pytest-of-%s' % getpass.getuser())
-                except ImportError:
-                    # see issue #1010
-                    rootdir = temproot.join('pytest-tox')
+                rootdir = temproot.join('pytest-of-%s' % get_user())
                 rootdir.ensure(dir=1)
                 basetemp = py.path.local.make_numbered_dir(prefix='pytest-',
                                                            rootdir=rootdir)
@@ -71,6 +66,18 @@ class TempdirFactory:
     def finish(self):
         self.trace("finish")
 
+
+def get_user():
+    """Return the current user name, falling back to using "tox" as user name
+    because getpass relies on environment variables which might not be
+    available in a tox environment (see #1010).
+    """
+    import getpass
+    try:
+        return getpass.getuser()
+    except ImportError:
+        return 'tox'
+
 # backward compatibility
 TempdirHandler = TempdirFactory
 
diff --git a/testing/test_tmpdir.py b/testing/test_tmpdir.py
index 0ea8e5263..2dc070bd6 100644
--- a/testing/test_tmpdir.py
+++ b/testing/test_tmpdir.py
@@ -133,3 +133,13 @@ def test_tmpdir_fallback_tox_env(testdir, monkeypatch):
     """)
     reprec = testdir.inline_run()
     reprec.assertoutcome(passed=1)
+
+
+def test_get_user(monkeypatch):
+    """Test that get_user() function works even if environment variables
+    required by getpass module are missing from the environment (#1010).
+    """
+    from _pytest.tmpdir import get_user
+    monkeypatch.delenv('USER', raising=False)
+    monkeypatch.delenv('USERNAME', raising=False)
+    assert get_user() == 'tox'