diff --git a/bin/python/isc/dnskey.py.in b/bin/python/isc/dnskey.py.in
index a95eb41660..605f03ef7c 100644
--- a/bin/python/isc/dnskey.py.in
+++ b/bin/python/isc/dnskey.py.in
@@ -90,7 +90,7 @@ class dnskey:
                 self.sep = False
         kfp.close()
 
-        pfp = open(private_file, "rU")
+        pfp = open(private_file, "r")
 
         self.metadata = dict()
         self._changed = dict()