diff --git a/Lib/python/pyrun.swg b/Lib/python/pyrun.swg
index 5eedca483..d43b75202 100644
--- a/Lib/python/pyrun.swg
+++ b/Lib/python/pyrun.swg
@@ -569,6 +569,7 @@ SwigPyObject_append(PyObject* v, PyObject* next)
   next = tmp;
 #endif
   if (!SwigPyObject_Check(next)) {
+    PyErr_SetString(PyExc_TypeError, "Attempt to append a non SwigPyObject");
     return NULL;
   }
   sobj->next = next;