diff --git a/openfold/np/protein.py b/openfold/np/protein.py
index 96d337b3..09b48cc5 100644
--- a/openfold/np/protein.py
+++ b/openfold/np/protein.py
@@ -254,7 +254,7 @@ def add_pdb_headers(prot: Protein, pdb_str: str) -> str:
     parents_per_chain = None
     if(prot.parents is not None):
         parents_per_chain = []
-        if(prot.parents_chain_index is not None):
+        if(prot.parents_chain_index is not None and len(prot.parents_chain_index) > 0):
             cur_chain = prot.parents_chain_index[0]
             parent_dict = {}
             for p, i in zip(prot.parents, prot.parents_chain_index):