diff --git a/tools/tui/loop/api.go b/tools/tui/loop/api.go
index 51396f911..1ac92c8fd 100644
--- a/tools/tui/loop/api.go
+++ b/tools/tui/loop/api.go
@@ -223,9 +223,12 @@ func (self *Loop) Println(args ...any) {
 }
 
 func (self *Loop) style_region(style string, start_x, start_y, end_x, end_y int) string {
-	sgr := self.SprintStyled(style, "|")[2:]
-	sgr = sgr[:strings.IndexByte(sgr, 'm')]
-	return fmt.Sprintf("\x1b[%d;%d;%d;%d;%s$r", start_y+1, start_x+1, end_y+1, end_x+1, sgr)
+	sgr := self.SprintStyled(style, "|")
+	if len(sgr) > 2 {
+		sgr = sgr[2:strings.IndexByte(sgr, 'm')]
+		return fmt.Sprintf("\x1b[%d;%d;%d;%d;%s$r", start_y+1, start_x+1, end_y+1, end_x+1, sgr)
+	}
+	return ""
 }
 
 // Apply the specified style to the specified region of the screen (0-based