diff --git a/tensornetwork/backends/numpy/numpy_backend.py b/tensornetwork/backends/numpy/numpy_backend.py
index 2d3753911..9f1a9220a 100644
--- a/tensornetwork/backends/numpy/numpy_backend.py
+++ b/tensornetwork/backends/numpy/numpy_backend.py
@@ -604,7 +604,9 @@ def sum(self,
           tensor: Tensor,
           axis: Optional[Sequence[int]] = None,
           keepdims: bool = False) -> Tensor:
-    return np.sum(tensor, axis=tuple(axis), keepdims=keepdims)
+          if axis is not None and type(axis) == list:
+            return np.sum(tensor, axis=tuple(axis), keepdims=keepdims)
+          return np.sum(tensor, axis=axis, keepdims=keepdims)
 
   def matmul(self, tensor1: Tensor, tensor2: Tensor) -> Tensor:
     if (tensor1.ndim <= 1) or (tensor2.ndim <= 1):