diff --git a/src/operator/nn/lrn.cc b/src/operator/nn/lrn.cc
index 6b3d7c818378..25670820f9e7 100644
--- a/src/operator/nn/lrn.cc
+++ b/src/operator/nn/lrn.cc
@@ -198,6 +198,7 @@ number of kernels in the layer.
 .add_arguments(LRNParam::__FIELDS__());
 
 NNVM_REGISTER_OP(_backward_LRN)
+.set_num_inputs(3)
 .set_num_outputs(1)
 .set_attr_parser(ParamParser<LRNParam>)
 .set_attr<FInferStorageType>("FInferStorageType", LRNBackwardInferStorageType)