diff --git a/imperative/python/megengine/core/tensor/megbrain_graph.py b/imperative/python/megengine/core/tensor/megbrain_graph.py
index 818d119e..cc4a4f4e 100644
--- a/imperative/python/megengine/core/tensor/megbrain_graph.py
+++ b/imperative/python/megengine/core/tensor/megbrain_graph.py
@@ -11,6 +11,8 @@ import threading
 import weakref
 from concurrent.futures import Future, ThreadPoolExecutor
 
+import numpy as np
+
 from .. import _imperative_rt
 from .._imperative_rt.ops import BackwardGraph
 from .._wrap import device as as_device
@@ -32,6 +34,8 @@ class Graph(_imperative_rt.ComputingGraph):
             wrapper, cache = VarNode, self._var_cache
         elif type(obj) is _imperative_rt.OperatorNode:
             wrapper, cache = OpNode, self._op_cache
+        else:
+            raise TypeError(type(obj))
         if obj not in cache:
             cache[obj] = wrapper(obj)
         return cache[obj]
@@ -62,6 +66,11 @@ class Graph(_imperative_rt.ComputingGraph):
             assert dtype is None and device is None
             return self._wrap(_imperative_rt.make_shared(self, data))
         else:
+            data = np.asarray(data, dtype=dtype)
+            if data.dtype == np.float64:
+                data = data.astype(np.float32)
+            elif data.dtype == np.int64:
+                data = data.astype(np.int32)
             device = as_device(device).to_c()
             return self._wrap(_imperative_rt.make_const(self, data, device, dtype))
 
diff --git a/imperative/python/src/graph_rt.cpp b/imperative/python/src/graph_rt.cpp
index 38b2b3b5..67de3508 100644
--- a/imperative/python/src/graph_rt.cpp
+++ b/imperative/python/src/graph_rt.cpp
@@ -181,10 +181,10 @@ void init_graph_rt(py::module m) {
 
     m.def("make_const", [](cg::ComputingGraph* graph, py::array data, CompNode cn, DType dtype) {
             if (!cn.valid()) {
-                throw py::type_error("device must not be None");
+                cn = CompNode::load("xpux");
             }
             auto hv = npy::np2tensor(data.ptr(), npy::Meth::borrow(cn), dtype);
-            opr::ImmutableTensor::make(*graph, hv, OperatorNodeConfig(cn)).node();
+            return opr::ImmutableTensor::make(*graph, hv, OperatorNodeConfig(cn)).node();
         });
 
     m.def("input_callback", [input_callback](std::function<DeviceTensorND(void)> callback,