diff --git a/autoload/slime/targets/tmux.vim b/autoload/slime/targets/tmux.vim
index 1a9b27d..91b8313 100644
--- a/autoload/slime/targets/tmux.vim
+++ b/autoload/slime/targets/tmux.vim
@@ -24,8 +24,8 @@ function! slime#targets#tmux#send(config, text)
   " reasonable hardcode, will become config if needed
   let chunk_size = 1000
 
-  for i in range(0, len(text_to_paste) / chunk_size)
-    let chunk = text_to_paste[i * chunk_size : (i + 1) * chunk_size - 1]
+  for i in range(0, strchars(text_to_paste) / chunk_size)
+    let chunk = strcharpart(text_to_paste, i * chunk_size, chunk_size)
     call slime#common#system(target_cmd . " load-buffer -", [], chunk)
     if bracketed_paste
       call slime#common#system(target_cmd . " paste-buffer -d -p -t %s", [a:config["target_pane"]])