diff --git a/example/ck_tile/18_hstu_attention/hstu_block_masking.hpp b/example/ck_tile/18_hstu_attention/hstu_block_masking.hpp
index 37d2ea8751..d6a7290e1b 100644
--- a/example/ck_tile/18_hstu_attention/hstu_block_masking.hpp
+++ b/example/ck_tile/18_hstu_attention/hstu_block_masking.hpp
@@ -275,8 +275,11 @@ struct HstuBlockMaskWithLocal
             index_t i_tile_right  = i_tile_left + TileWidth;
             index_t i_tile_bottom = i_tile_top + TileHeight;
 
-            if(!is_tile_in_first_split && i_tile_bottom <= max_uih_len &&
-               i_tile_right <= i_tile_top + 1)
+            // 1) tile is completely in [max_uih_len-min_full_attn_seqlen, max_uih_len]
+            // 2) some row of tile is in [max_uih_len, seqlen], requires i_tile_right <= max_uih_len
+            // to return true
+            if(!is_tile_in_first_split &&
+               (i_tile_bottom <= max_uih_len || i_tile_right <= max_uih_len))
                 return true;
         };