diff --git a/imperative/python/test/unit/functional/test_math.py b/imperative/python/test/unit/functional/test_math.py
index e0765c8d..a8f10326 100644
--- a/imperative/python/test/unit/functional/test_math.py
+++ b/imperative/python/test/unit/functional/test_math.py
@@ -7,6 +7,8 @@ from utils import opr_test
 
 import megengine.functional as F
 from megengine import jit, tensor
+from megengine.core._imperative_rt.core2 import apply
+from megengine.core.ops import builtin
 
 
 def common_test_reduce(opr, ref_opr):
@@ -182,6 +184,21 @@ def test_sum_neg_axis():
         F.sum(tensor(data), axis=(-1, 1))
 
 
+def test_builtin_reduce():
+    shape = (2, 3, 3, 2)
+    data = np.random.random(shape).astype(np.float32)
+    for axis in (-1, -2, 0, 1):
+        for keepdims in (True, False):
+            op = builtin.Reduce(mode="sum", axis=axis, keepdim=keepdims)
+            get = apply(op, tensor(data))[0]
+            def_op = builtin.Reduce(mode="sum", axis=axis)
+            def_get = apply(def_op, tensor(data))[0]
+            ref = np.sum(data, axis=axis, keepdims=keepdims)
+            np.testing.assert_allclose(get.numpy(), ref, rtol=1e-6)
+            if keepdims == True:
+                np.testing.assert_allclose(def_get.numpy(), ref, rtol=1e-6)
+
+
 def test_non_finite():
     shape = (32, 3, 32, 32)
     data = []
diff --git a/imperative/src/impl/ops/reduce.cpp b/imperative/src/impl/ops/reduce.cpp
index dc4595f1..f50bef0f 100644
--- a/imperative/src/impl/ops/reduce.cpp
+++ b/imperative/src/impl/ops/reduce.cpp
@@ -222,7 +222,7 @@ std::tuple<SmallVector<LogicalTensorDesc>, bool> infer_output_attrs_fallible(
         for (size_t i = 0; i < size; ++i) {
             dests[i].comp_node = inputs[i].comp_node;
             dests[i].layout = inputs[i].layout;
-            if (not keepdim && dests[i].layout.ndim > 1) {
+            if (!keepdim && dests[i].layout.ndim > 1) {
                 dests[i].layout.remove_axis_inplace(axis);
             } else {
                 dests[i].layout.shape[axis] = 1;
diff --git a/src/core/include/megbrain/ir/ops.td b/src/core/include/megbrain/ir/ops.td
index 3100df70..4d8dff62 100644
--- a/src/core/include/megbrain/ir/ops.td
+++ b/src/core/include/megbrain/ir/ops.td
@@ -16,7 +16,7 @@ def Elemwise : MgbHashableOp<"Elemwise", [ElemwiseParam], [NoSideEffect]> {
 
 def Reduce: MgbHashableOp<"Reduce", [ReduceParam]>{
   let extraArguments = (ins
-    MgbBoolAttr:$keepdim
+    MgbDefaultValuedAttr<MgbBoolAttr, "true">:$keepdim
   );
 }