diff --git a/tests/test_context.py b/tests/test_context.py
index 8e73894..bd8e2e7 100644
--- a/tests/test_context.py
+++ b/tests/test_context.py
@@ -158,6 +158,7 @@ def test_distrib_with_cache_with_all_facets(self):
         self._test_distrib(constraints=self._distrib_constraints_all_facets,
                            cache=self.cache)
 
+    @pytest.mark.xfail("may sometimes fail if server returns incomplete set of results")
     def test_constrain(self):
         conn = SearchConnection(self.test_service, cache=self.cache)
 
@@ -186,6 +187,7 @@ def test_constrain_regression1(self):
         context2 = context.constrain(experiment='historical')
         self.assertTrue('experiment' in context2.facet_constraints)
 
+    @pytest.mark.xfail("may sometimes fail if server returns incomplete set of results")
     def test_negative_facet(self):
         conn = SearchConnection(self.test_service, cache=self.cache)