diff --git a/dimorphite_dl.py b/dimorphite_dl.py
index 73719b1..2dadad1 100644
--- a/dimorphite_dl.py
+++ b/dimorphite_dl.py
@@ -713,11 +713,8 @@ def load_substructre_smarts_file():
 
         pwd = os.path.dirname(os.path.realpath(__file__))
         site_structures_file = "{}/{}".format(pwd, "site_substructures.smarts")
-        lines = [
-            l
-            for l in open(site_structures_file, "r")
-            if l.strip() != "" and not l.startswith("#")
-        ]
+        with open(site_structures_file, "r") as f:
+            lines = [l for l in f if l.strip() != "" and not l.startswith("#")]
 
         return lines