diff --git a/IPython/utils/tests/test_jsonutil.py b/IPython/utils/tests/test_jsonutil.py
index cb79f80..45247a0 100644
--- a/IPython/utils/tests/test_jsonutil.py
+++ b/IPython/utils/tests/test_jsonutil.py
@@ -58,7 +58,8 @@ def test():
 
 def test_lambda():
     jc = json_clean(lambda : 1)
-    nt.assert_true(jc.startswith('<function <lambda> at '))
+    assert isinstance(jc, str)
+    assert '<lambda>' in jc
     json.dumps(jc)