diff --git a/layers/output_utils.py b/layers/output_utils.py
index 27efac935..57670ee77 100644
--- a/layers/output_utils.py
+++ b/layers/output_utils.py
@@ -85,7 +85,8 @@ def postprocess(det_output, w, h, batch_idx=0, interpolation_mode='bilinear',
                         if cfg.rescore_bbox:
                             scores = scores * maskiou_p
                         else:
-                            scores = [scores, scores * maskiou_p]
+                            scores = np.concatenate(
+                                (scores, scores * maskiou_p))
 
         # Scale masks up to the full image
         masks = F.interpolate(masks.unsqueeze(0), (h, w), mode=interpolation_mode, align_corners=False).squeeze(0)