diff --git a/_pytest/tmpdir.py b/_pytest/tmpdir.py
index 44e980e2e..b90e35948 100644
--- a/_pytest/tmpdir.py
+++ b/_pytest/tmpdir.py
@@ -52,11 +52,14 @@ class TempdirFactory:
                     basetemp.remove()
                 basetemp.mkdir()
             else:
-                # use a sub-directory in the temproot to speed-up
-                # make_numbered_dir() call
-                import getpass
                 temproot = py.path.local.get_temproot()
-                rootdir = temproot.join('pytest-of-%s' % getpass.getuser())
+                user = get_user()
+                if user:
+                    # use a sub-directory in the temproot to speed-up
+                    # make_numbered_dir() call
+                    rootdir = temproot.join('pytest-of-%s' % user)
+                else:
+                    rootdir = temproot
                 rootdir.ensure(dir=1)
                 basetemp = py.path.local.make_numbered_dir(prefix='pytest-',
                                                            rootdir=rootdir)
@@ -67,6 +70,17 @@ class TempdirFactory:
     def finish(self):
         self.trace("finish")
 
+
+def get_user():
+    """Return the current user name, or None if getuser() does not work
+    in the current environment (see #1010).
+    """
+    import getpass
+    try:
+        return getpass.getuser()
+    except ImportError:
+        return None
+
 # backward compatibility
 TempdirHandler = TempdirFactory
 
diff --git a/testing/test_tmpdir.py b/testing/test_tmpdir.py
index 05b24fc59..9bc0cf40a 100644
--- a/testing/test_tmpdir.py
+++ b/testing/test_tmpdir.py
@@ -1,3 +1,4 @@
+import sys
 import py
 import pytest
 
@@ -117,4 +118,31 @@ def test_tmpdir_factory(testdir):
             session_dir.isdir()
     """)
     reprec = testdir.inline_run()
-    reprec.assertoutcome(passed=1)
\ No newline at end of file
+    reprec.assertoutcome(passed=1)
+
+
+def test_tmpdir_fallback_tox_env(testdir, monkeypatch):
+    """Test that tmpdir works even if environment variables required by getpass
+    module are missing (#1010).
+    """
+    monkeypatch.delenv('USER', raising=False)
+    monkeypatch.delenv('USERNAME', raising=False)
+    testdir.makepyfile("""
+        import pytest
+        def test_some(tmpdir):
+            assert tmpdir.isdir()
+    """)
+    reprec = testdir.inline_run()
+    reprec.assertoutcome(passed=1)
+
+
+@pytest.mark.skipif(not sys.platform.startswith('win'), reason='win only')
+def test_get_user(monkeypatch):
+    """Test that get_user() function works even if environment variables
+    required by getpass module are missing from the environment on Windows
+    (#1010).
+    """
+    from _pytest.tmpdir import get_user
+    monkeypatch.delenv('USER', raising=False)
+    monkeypatch.delenv('USERNAME', raising=False)
+    assert get_user() is None