diff --git a/ippisite/ippidb/ws.py b/ippisite/ippidb/ws.py
index 7a272f2a30e659ae65b408f4825b2085c2c3a9d4..b29027bbaac1d15404f731141790191189ffd380 100644
--- a/ippisite/ippidb/ws.py
+++ b/ippisite/ippidb/ws.py
@@ -80,6 +80,6 @@ def get_pfam_info(pfam_acc):
             'description': description}
 
 def get_pdb_uniprot_mapping(pdb_id):
-    resp = requests.get('https://www.ebi.ac.uk/pdbe/api/mappings/uniprot/{}'.format(pdb_id))
+    resp = requests.get('https://www.ebi.ac.uk/pdbe/api/mappings/uniprot/{}'.format(pdb_id.lower()))
     uniprot_ids = list(resp.json()[pdb_id]['UniProt'].keys())
     return uniprot_ids