diff --git a/src/.gdbinit b/src/.gdbinit
index e9bb716a091..b2395e9e3c9 100644
--- a/src/.gdbinit
+++ b/src/.gdbinit
@@ -158,7 +158,7 @@ end
 
 define xstring
 print (struct Lisp_String *) (($ & $valmask) | gdb_data_seg_bits)
-output ($->size > 1000) ? 0 : ($->data[0])@($->size)
+output ($->size > 1000) ? 0 : ($->data[0])@($->size_byte)
 echo \n
 end
 document xstring