diff --git a/autoload/airline.vim b/autoload/airline.vim
index 77e81bd4..a4293b59 100644
--- a/autoload/airline.vim
+++ b/autoload/airline.vim
@@ -262,7 +262,7 @@ function! airline#check_mode(winnr)
   let mode_string = join(l:mode)
   if get(w:, 'airline_lastmode', '') != mode_string
     call airline#highlighter#highlight_modified_inactive(context.bufnr)
-    call airline#highlighter#highlight(l:mode, context.bufnr)
+    call airline#highlighter#highlight(l:mode, string(context.bufnr))
     call airline#util#doautocmd('AirlineModeChanged')
     let w:airline_lastmode = mode_string
   endif