diff --git a/forgi/threedee/utilities/modified_res.py b/forgi/threedee/utilities/modified_res.py
index 2e5ad29..9cc09a9 100644
--- a/forgi/threedee/utilities/modified_res.py
+++ b/forgi/threedee/utilities/modified_res.py
@@ -20,7 +20,7 @@
 
 
 from ...graph import residue as fgr
-import forgi.threedee.utilities.pdb as ftup
+
 #from .modified_res_lookup import RESIDUE_DICT
 
 log = logging.getLogger(__name__)
@@ -109,6 +109,7 @@ def to_4_letter_alphabeth(chain, query_db=False):
     :param query_db: If true, query PDBeChem whenever a 3-letter code is unknown.
     :return: The same chain, but with only AUGC residues.
     '''
+    import forgi.threedee.utilities.pdb as ftup
     modifications = {}
     i = 0
     while i < len(chain):