diff --git a/plug.vim b/plug.vim
index c41f1b9..f371f62 100644
--- a/plug.vim
+++ b/plug.vim
@@ -725,7 +725,7 @@ function! s:update_parallel(pull, todo, threads)
 
   def killall pid
     pids = [pid]
-    unless `which pgrep`.empty?
+    unless `which pgrep 2> /dev/null`.empty?
       children = pids
       until children.empty?
         children = children.map { |pid|