diff --git a/_pytest/tmpdir.py b/_pytest/tmpdir.py
index 44e980e2e..cff39065f 100644
--- a/_pytest/tmpdir.py
+++ b/_pytest/tmpdir.py
@@ -56,7 +56,11 @@ class TempdirFactory:
                 # make_numbered_dir() call
                 import getpass
                 temproot = py.path.local.get_temproot()
-                rootdir = temproot.join('pytest-of-%s' % getpass.getuser())
+                try:
+                    rootdir = temproot.join('pytest-of-%s' % getpass.getuser())
+                except ImportError:
+                    # see issue #1010
+                    rootdir = temproot.join('pytest-tox')
                 rootdir.ensure(dir=1)
                 basetemp = py.path.local.make_numbered_dir(prefix='pytest-',
                                                            rootdir=rootdir)
diff --git a/testing/test_tmpdir.py b/testing/test_tmpdir.py
index 05b24fc59..0ea8e5263 100644
--- a/testing/test_tmpdir.py
+++ b/testing/test_tmpdir.py
@@ -117,4 +117,19 @@ 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)