diff --git a/mace/core/operator.h b/mace/core/operator.h
index df488691bac3fd8de6aea9c98a7175f80b50f41e..4ec4e7b175af7ba2d6ff7af411ece348ecc6d9e7 100644
--- a/mace/core/operator.h
+++ b/mace/core/operator.h
@@ -44,7 +44,7 @@ class OperatorBase {
         *operator_def_, name, default_value);
   }
 
-  inline const Tensor *Input(index_t idx) {
+  inline const Tensor *Input(unsigned int idx) {
     MACE_CHECK(idx < inputs_.size());
     return inputs_[idx];
   }
diff --git a/mace/core/tensor.h b/mace/core/tensor.h
index 1af32d3f2338f344332375d9cb67cbe23a4f119d..d40d39d78220bc0e470ddc799debb2b645923dce 100644
--- a/mace/core/tensor.h
+++ b/mace/core/tensor.h
@@ -68,9 +68,8 @@ class Tensor {
 
   inline index_t dim_size() const { return shape_.size(); }
 
-  inline index_t dim(index_t index) const {
+  inline index_t dim(unsigned int index) const {
     MACE_CHECK(index < shape_.size(), "Exceeding ndim limit");
-    MACE_CHECK(index >= 0, "Cannot have negative dimension index");
     return shape_[index];
   }