Index: test/shell1.test
==================================================================
--- test/shell1.test
+++ test/shell1.test
@@ -903,11 +903,16 @@
     set res [lindex $x 1]
     if {$code ne "0"} {
       error "failed with error: $res"
     }
     if {$res ne "$oldChar\n"} {
-      error "failed with byte $hex mismatch"
+      if {[llength $res] > 0} {
+        set got [format %02X [scan $res %c]]
+      } else {
+        set got <empty>
+      }
+      error "failed with byte $hex mismatch, got $got"
     }
   }
 } {}
 
 # The string used here is the word "test" in Chinese.