diff --git a/lib/iris/tests/unit/analysis/test_PERCENTILE.py b/lib/iris/tests/unit/analysis/test_PERCENTILE.py
index c1d3996309..e4bdef0fa7 100644
--- a/lib/iris/tests/unit/analysis/test_PERCENTILE.py
+++ b/lib/iris/tests/unit/analysis/test_PERCENTILE.py
@@ -162,7 +162,7 @@ def test_default_kwargs_passed(self, mocked_mquantiles):
         for key in ["alphap", "betap"]:
             self.assertEqual(mocked_mquantiles.call_args.kwargs[key], 1)
 
-    @mock.patch("scipy.stats.mstats.mquantiles")
+    @mock.patch("scipy.stats.mstats.mquantiles", return_value=np.array([2, 4]))
     def test_chosen_kwargs_passed(self, mocked_mquantiles):
         data = np.arange(5)
         percent = [42, 75]
@@ -356,7 +356,7 @@ def test_numpy_percentile_called(self, mocked_percentile):
         # Check we have left "method" keyword to numpy's default.
         self.assertNotIn("method", mocked_percentile.call_args.kwargs)
 
-    @mock.patch("numpy.percentile")
+    @mock.patch("numpy.percentile", return_value=np.array([2, 4]))
     def test_chosen_method_kwarg_passed(self, mocked_percentile):
         data = da.arange(5)
         percent = [42, 75]