diff --git a/fastNLP/modules/encoder/star_transformer.py b/fastNLP/modules/encoder/star_transformer.py
index b28d3d1d..809948bb 100644
--- a/fastNLP/modules/encoder/star_transformer.py
+++ b/fastNLP/modules/encoder/star_transformer.py
@@ -57,6 +57,7 @@ class StarTransformer(nn.Module):
         nodes = embs
         relay = embs.mean(2, keepdim=True)
         ex_mask = mask[:, None, :, None].expand(B, H, L, 1)
+        ex_mask = ex_mask.ne(1) # reverse mask for next masked_fill.
         r_embs = embs.view(B, H, 1, L)
         for i in range(self.iters):
             ax = torch.cat([r_embs, relay.expand(B, H, 1, L)], 2)