--- loncom/lonnet/perl/lonnet.pm	2018/12/05 21:36:18	1.1393
+++ loncom/lonnet/perl/lonnet.pm	2018/12/08 15:17:25	1.1394
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # TCP networking package
 #
-# $Id: lonnet.pm,v 1.1393 2018/12/05 21:36:18 raeburn Exp $
+# $Id: lonnet.pm,v 1.1394 2018/12/08 15:17:25 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -711,6 +711,7 @@ sub check_for_valid_session {
 
     if (!defined($disk_env{'user.name'})
 	|| !defined($disk_env{'user.domain'})) {
+        untie(%disk_env);
 	return undef;
     }
 
@@ -723,6 +724,7 @@ sub check_for_valid_session {
             $userhashref->{'ltiuri'} = $disk_env{'request.lti.uri'};
         }
     }
+    untie(%disk_env);
 
     return $handle;
 }