diff --git a/python/tvm/tir/expr.py b/python/tvm/tir/expr.py
index deb8d3446fc1..a192fce6439a 100644
--- a/python/tvm/tir/expr.py
+++ b/python/tvm/tir/expr.py
@@ -370,7 +370,8 @@ def __init__(self, dom, var, iter_type, thread_tag=""):
                 raise TypeError("dom need to be Range")
 
         name = var if var is not None else "iter"
-        var = Var(name, dtype="int32") if not isinstance(var, Var) else var
+        dtype = "int32" if dom is None else dom.extent.dtype
+        var = Var(name, dtype=dtype) if not isinstance(var, Var) else var
         self.__init_handle_by_constructor__(
             _ffi_api.IterVar, dom, var, iter_type, thread_tag)
 
diff --git a/src/tir/pass/narrow_datatype.cc b/src/tir/pass/narrow_datatype.cc
index d376e41d1e64..e6bc43abf7cb 100644
--- a/src/tir/pass/narrow_datatype.cc
+++ b/src/tir/pass/narrow_datatype.cc
@@ -31,7 +31,7 @@ namespace tvm {
 namespace tir {
 
 // This pass narrows indexing expressions (like StoreNode::Index)
-// that trivially fit into i32/i16 (denoted by `target_bits_`) to 
+// that trivially fit into i32/i16 (denoted by `target_bits_`) to
 // i32/i16. Considering that i32/i16 indices may be more
 // efficient on some backends (while i64 may be more efficient
 // on others, like llvm), we may want this pass when i32/i16
@@ -62,7 +62,7 @@ using arith::ConstIntBound;
 //
 // Algorithm:
 // We propogate the dtypes of all the Exprs that contain Var `var` into `vmap[var]`.
-// To be more specific, if for each Expr `e` which contains `var` 
+// To be more specific, if for each Expr `e` which contains `var`
 // (`var` is a child node of `e` in AST), `e` fits into `target_bits_`,
 // then we narrow `var` into `target_bits_`. That is,
 // `vmap[var] = min(target_bits_, var.dtype.bits())`
diff --git a/tests/python/unittest/test_tir_pass_narrow_datatype.py b/tests/python/unittest/test_tir_pass_narrow_datatype.py
index 85b3f63261dd..96a8ef41f793 100644
--- a/tests/python/unittest/test_tir_pass_narrow_datatype.py
+++ b/tests/python/unittest/test_tir_pass_narrow_datatype.py
@@ -157,6 +157,7 @@ def check(m, target_bits, target_dtype):
 
 def test_slice():
     def check(m, n, target_bits, target_dtype):
+        # The index may overflow in B, while not in A
         ib = tvm.tir.ir_builder.create()
         Ab = tvm.tir.decl_buffer((m, n), name='A')
         A = ib.buffer_ptr(Ab)