diff --git a/groundingdino/util/utils.py b/groundingdino/util/utils.py
index 8cf83ae0..33f34748 100644
--- a/groundingdino/util/utils.py
+++ b/groundingdino/util/utils.py
@@ -601,7 +601,8 @@ def get_phrases_from_posmap(
 ):
     assert isinstance(posmap, torch.Tensor), "posmap must be torch.Tensor"
     if posmap.dim() == 1:
-        posmap[0: left_idx + 1] = False
+        if right_idx>left_idx:
+            posmap[0: left_idx + 1] = False
         posmap[right_idx:] = False
         non_zero_idx = posmap.nonzero(as_tuple=True)[0].tolist()
         token_ids = [tokenized["input_ids"][i] for i in non_zero_idx]