diff --git a/lib/tty/reader/line.rb b/lib/tty/reader/line.rb
index fb2bc57..490fadd 100644
--- a/lib/tty/reader/line.rb
+++ b/lib/tty/reader/line.rb
@@ -75,7 +75,7 @@ def prompt_display_width
 
         # return the length of each line + screen width for every line
         # past the first which accounts for multi-line prompts
-        lines.join.length + ((lines.length - 1) * TTY::Screen.width)
+        lines.last.length + ((lines.length - 1) * TTY::Screen.width)
       end
 
       # Check if line is in edit mode