diff --git a/paddle/py_paddle/util.py b/paddle/py_paddle/util.py
index 8ebcb346100c297948e0eb9a147c866f6bbca15d..e1f310580f95cfb210ba89589bab668433818b23 100644
--- a/paddle/py_paddle/util.py
+++ b/paddle/py_paddle/util.py
@@ -82,10 +82,10 @@ class __ParameterCallbackWrapper__(swig_paddle.UpdateCallback):
 def __arguments_to_numpy__(i, arg):
     assert isinstance(arg, swig_paddle.Arguments)
     value = arg.getSlotValue(i)
+    ids = arg.getSlotIds(i)
     if value is not None:
         assert isinstance(value, swig_paddle.Matrix)
         value = value.copyToNumpyMat()
-        ids = arg.getSlotIds(i)
     if ids is not None:
         assert isinstance(ids, swig_paddle.IVector)
         ids = ids.copyToNumpyArray()