diff --git a/tcl/drivers/ah2550.tcl b/tcl/drivers/ah2550.tcl
index 4cdd9d2..de3beef 100644
--- a/tcl/drivers/ah2550.tcl
+++ b/tcl/drivers/ah2550.tcl
@@ -46,7 +46,7 @@ proc ah2550::start {} {
 
 proc ah2550::start1 {} {
   set prefix [lindex [sct result] 0]
-  if {$prefix eq "UN"} { # this was the echo
+  if {[string match "*UN" $prefix]} { # this was the echo
     sct send "SERIAL ECHO OFF"
     return ah2550::start
   }
@@ -74,7 +74,7 @@ proc ah2550::update {} {
   set res [string map {"=" "= "} $res]
   #clientput $res
   lassign $res  prefix c _ _ _ l un _ _ v _ _ _ _ _ _ _
-  if {$prefix eq "SI"} {
+  if {[string match "*SI" $prefix]} {
     sct send "\r\nSERIAL ECHO OFF\r"
     return stdSct::complete
   }