diff --git a/tests/run.py b/tests/run.py
index 8b3bf844d..4cd4a7660 100755
--- a/tests/run.py
+++ b/tests/run.py
@@ -18,14 +18,14 @@ if sys.version_info >= (3, 0):
     from distutils.util import copydir_run_2to3
     testroot = path.dirname(__file__) or '.'
     if 'BUILD_TEST_PATH' in environ:
-        # for tox test.
+        # for tox testing
         newroot = environ['BUILD_TEST_PATH']
-        # tox install sphinx package, not need sys.path.insert.
+        # tox installs the sphinx package, no need for sys.path.insert
     else:
         newroot = path.join(testroot, path.pardir, 'build')
         newroot = path.join(newroot, listdir(newroot)[0], 'tests')
         # always test the sphinx package from build/lib/
-        sys.path.insert(0, path.join(newroot, path.pardir))
+        sys.path.insert(0, path.abspath(path.join(newroot, path.pardir)))
     copydir_run_2to3(testroot, newroot)
     # switch to the converted dir so nose tests the right tests
     chdir(newroot)