diff --git a/src/operator/roi_pooling.cu b/src/operator/roi_pooling.cu
index 38f5d67db5d5..5d972a457b15 100644
--- a/src/operator/roi_pooling.cu
+++ b/src/operator/roi_pooling.cu
@@ -205,7 +205,7 @@ inline void ROIPoolBackwardAcc(const Tensor<gpu, 4, Dtype> &in_grad,
   Dtype *bottom_diff = in_grad.dptr_;
   Dtype *argmax_data = max_idx.dptr_;
   const int count = in_grad.shape_.Size();
-  const int num_rois = bbox.size(1);
+  const int num_rois = bbox.size(0) * bbox.size(1);
   const int channels = in_grad.size(1);
   const int height = in_grad.size(2);
   const int width = in_grad.size(3);