diff --git a/src/conio/cterm.c b/src/conio/cterm.c
index f1601ae1b91cedbb150c28f57b76d2d7898dcd2b..17c0bae1c0b3f259dffd2fbccaa82d0349405a32 100644
--- a/src/conio/cterm.c
+++ b/src/conio/cterm.c
@@ -2153,7 +2153,7 @@ do_backtab(struct cterminal *cterm)
 
 	CURR_XY(&cx, &cy);
 	ox = cx;
-	for (i = cterm->tab_count; i >= 0; i--) {
+	for (i = cterm->tab_count - 1; i >= 0; i--) {
 		if (cterm->tabs[i] < cx) {
 			cx = cterm->tabs[i];
 			break;