diff --git a/os_testr/regex_builder.py b/os_testr/regex_builder.py
index 8f5261e..abc08fc 100644
--- a/os_testr/regex_builder.py
+++ b/os_testr/regex_builder.py
@@ -19,7 +19,10 @@ import subprocess
 
 def _get_test_list(regex, env=None):
     env = env or copy.deepcopy(os.environ)
-    proc = subprocess.Popen(['testr', 'list-tests', regex], env=env,
+    testr_args = ['testr', 'list-tests']
+    if regex:
+        testr_args.append(regex)
+    proc = subprocess.Popen(testr_args, env=env,
                             stdout=subprocess.PIPE, universal_newlines=True)
     out = proc.communicate()[0]
     raw_test_list = out.split('\n')
diff --git a/os_testr/tests/test_regex_builder.py b/os_testr/tests/test_regex_builder.py
index 04a9748..c78500c 100644
--- a/os_testr/tests/test_regex_builder.py
+++ b/os_testr/tests/test_regex_builder.py
@@ -174,3 +174,16 @@ class TestGetTestList(base.TestCase):
     def test__get_test_list(self):
         test_list = os_testr._get_test_list('test__get_test_list')
         self.assertIn('test__get_test_list', test_list[0])
+
+    def test__get_test_list_regex_is_empty(self):
+        test_list = os_testr._get_test_list('')
+        self.assertIn('', test_list[0])
+
+    def test__get_test_list_regex_is_none(self):
+        test_list = os_testr._get_test_list(None)
+        # NOTE(masayukig): We should get all of the tests. So we should have
+        # more than one test case.
+        self.assertGreater(len(test_list), 1)
+        self.assertIn('os_testr.tests.test_regex_builder.'
+                      'TestGetTestList.test__get_test_list_regex_is_none',
+                      test_list)