diff --git a/src/fenrir/screenDriver/vcsaDriver.py b/src/fenrir/screenDriver/vcsaDriver.py
index 5330bd24..25ca4680 100644
--- a/src/fenrir/screenDriver/vcsaDriver.py
+++ b/src/fenrir/screenDriver/vcsaDriver.py
@@ -324,6 +324,8 @@ class driver(screenDriver):
             self.env['screen']['newCursorAttrib'] = None            
             self.env['screen']['oldNegativeDelta'] = ''
         # initialize current deltas
+        if self.env['screen']['oldTTY'] == None:
+            self.env['screen']['oldTTY'] = self.env['screen']['newTTY']
         self.env['screen']['newNegativeDelta'] = ''
         self.env['screen']['newDelta'] = ''
         self.env['screen']['newAttribDelta'] = ''