diff --git a/mrdna/readers/segmentmodel_from_oxdna_pinyi.py b/mrdna/readers/segmentmodel_from_oxdna_pinyi.py
index b50d5685f5496ff61b037f880ddf82c18fcaa6dd..bf50368531592f41566aa31db8bcea8dd406c58e 100644
--- a/mrdna/readers/segmentmodel_from_oxdna_pinyi.py
+++ b/mrdna/readers/segmentmodel_from_oxdna_pinyi.py
@@ -96,6 +96,7 @@ def mrdna_model_from_oxdna(coordinate_file, topology_file,virt2nuc=None,get_nt_p
         L1=_find_vh_vb_table(vh_vb._scaf,1)
         L2=_find_vh_vb_table(vh_vb._stap,0)
         nt_prop=pd.DataFrame(L1+L2,dtype=object)
+        nt_prop["index"]=nt_prop["index"].astype(int)
         nt_prop.set_index("index",inplace=True)
         nt_prop.sort_index(inplace=True)
         nt_prop["threeprime"]=top_data[2]