diff --git a/include/mlir-hlo/Dialect/mhlo/IR/lhlo_ops.td b/include/mlir-hlo/Dialect/mhlo/IR/lhlo_ops.td
index 0ee44f3..ff052b5 100644
--- a/include/mlir-hlo/Dialect/mhlo/IR/lhlo_ops.td
+++ b/include/mlir-hlo/Dialect/mhlo/IR/lhlo_ops.td
@@ -197,10 +197,11 @@ def LHLO_XorOp : LHLO_BinaryElementwiseOp<"xor", LHLO_PredOrIntBuffer>, BASE_HLO
 //===----------------------------------------------------------------------===//
 
 // TODO(b/139813999): specify required function signature in a type-safe way.
-def LHLO_ReduceOp: LHLO_Op<"reduce", [
-      SameVariadicOperandSize,
-      SingleBlockImplicitTerminator<"TerminatorOp">
-    ]>, BASE_HLO_ReduceOp {
+//
+// The region `body` may return lmhlo.TerminatorOp or mhlo.ReturnOp. We are
+// moving towards mhlo.ReturnOp, but some code that needs cleanup still assumes lmhlo.TerminatorOp.
+// TODO(timshen): cleanup lmhlo.TerminatorOp.
+def LHLO_ReduceOp: LHLO_Op<"reduce", [SameVariadicOperandSize]>, BASE_HLO_ReduceOp {
   let arguments = (ins
     Arg<Variadic<LHLO_Buffer>, "", [MemRead]>:$operands,
     Arg<Variadic<LHLO_Buffer>, "", [MemRead]>:$init_values,