diff --git a/mmdet/models/dense_heads/ssd_head.py b/mmdet/models/dense_heads/ssd_head.py
index ee773455d1f..e362fd8016a 100644
--- a/mmdet/models/dense_heads/ssd_head.py
+++ b/mmdet/models/dense_heads/ssd_head.py
@@ -316,7 +316,7 @@ def loss(self,
             gt_bboxes_ignore_list=gt_bboxes_ignore,
             gt_labels_list=gt_labels,
             label_channels=1,
-            unmap_outputs=False)
+            unmap_outputs=True)
         if cls_reg_targets is None:
             return None
         (labels_list, label_weights_list, bbox_targets_list, bbox_weights_list,