diff --git a/lib/nerdtree/ui.vim b/lib/nerdtree/ui.vim
index 094fa0f..d107814 100644
--- a/lib/nerdtree/ui.vim
+++ b/lib/nerdtree/ui.vim
@@ -282,7 +282,8 @@ endfunction
 function! s:UI._indentLevelFor(line)
     "have to do this work around because match() returns bytes, not chars
     let numLeadBytes = match(a:line, '\M\[^ '.g:NERDTreeDirArrowExpandable.g:NERDTreeDirArrowCollapsible.']')
-    let leadChars = strchars(a:line[0:numLeadBytes-1])
+    " The next line is a backward-compatible workaround for strchars(a:line(0:numLeadBytes-1]). strchars() is in 7.3+
+    let leadChars = len(split(a:line[0:numLeadBytes-1], '\zs'))
 
     return leadChars / s:UI.IndentWid()
 endfunction