diff --git a/daq/src/mxlibs3/tell_client.py b/daq/src/mxlibs3/tell_client.py
index 21cb98e5..61f9dcb3 100755
--- a/daq/src/mxlibs3/tell_client.py
+++ b/daq/src/mxlibs3/tell_client.py
@@ -31,7 +31,7 @@ class TellCommandWhileBusyException(Exception):
     pass
 
 
-VALID_DEWAR_POSITIONS = [f"{p}{n}" for n in "12345" for p in "ABCDEF"]
+VALID_DEWAR_POSITIONS = [f"{p}{n}" for n in "12345" for p in "ABCDEFX"]
 
 POSITION_PARK = "pPark"
 POSITION_COLD = "pCold"