diff --git a/src/JSObjectProxy.cc b/src/JSObjectProxy.cc
index 13b3e609..359b072d 100644
--- a/src/JSObjectProxy.cc
+++ b/src/JSObjectProxy.cc
@@ -320,6 +320,9 @@ PyObject *JSObjectProxyMethodDefinitions::JSObjectProxy_iter_next(JSObjectProxy
 
   PyObject *retVal = JSFunctionProxyMethodDefinitions::JSFunctionProxy_call(nextFunction, PyTuple_New(0), NULL);
   Py_DECREF(nextFunction);
+  if (retVal == NULL) {
+    return NULL;
+  }
 
   // check if end of iteration
   key = PyUnicode_FromString("done");
diff --git a/tests/python/test_dict_methods.py b/tests/python/test_dict_methods.py
index a303f73a..d0fccba9 100644
--- a/tests/python/test_dict_methods.py
+++ b/tests/python/test_dict_methods.py
@@ -555,3 +555,19 @@ def test_next_operator():
     assert (True)
   fourth = next(myit, 'default')
   assert fourth == 'default'
+
+
+def test_next_operator_non_iterator():
+  make_js_generator = pm.eval("""
+  function* sliceGenerator(pyIter)
+  {
+      yield python.eval('lambda x: next(x)')(pyIter);
+  }
+  sliceGenerator;
+  """)
+
+  try:
+    next(make_js_generator(range(0,5)))
+    assert (False)
+  except pm.SpiderMonkeyError as e:
+    assert "'range' object is not an iterator" in str(e)
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