diff --git a/src/ffi/ffi_infinitensor.cc b/src/ffi/ffi_infinitensor.cc
index f979b03c..c2d35051 100644
--- a/src/ffi/ffi_infinitensor.cc
+++ b/src/ffi/ffi_infinitensor.cc
@@ -95,17 +95,17 @@ static int tensor_dtype(Tensor t) {
 
 static int concat_axis_of(Operator op) {
     IT_ASSERT(op->getOpType() == OpType::Concat);
-    return reinterpret_cast<const ConcatObj *>(op.get())->getDim();
+    return dynamic_cast<const ConcatObj *>(op.get())->getDim();
 }
 
 static int gather_axis_of(Operator op) {
     IT_ASSERT(op->getOpType() == OpType::Gather);
-    return reinterpret_cast<const GatherObj *>(op.get())->getAxis();
+    return dynamic_cast<const GatherObj *>(op.get())->getAxis();
 }
 
 static Shape reshape_shape_of(Operator op) {
     IT_ASSERT(op->getOpType() == OpType::Reshape);
-    return reinterpret_cast<const ReshapeObj *>(op.get())->getShape();
+    return dynamic_cast<const ReshapeObj *>(op.get())->getShape();
 }
 
 void init_graph_builder(py::module &m) {