diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index 7d2c6231..0c2af5d9 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -656,7 +656,7 @@ def valid_pid?(path)
     wpid <= 0 and return
     Process.kill(0, wpid)
     wpid
-    rescue Errno::ESRCH, Errno::ENOENT
+    rescue Errno::ESRCH, Errno::ENOENT, Errno::EPERM
       # don't unlink stale pid files, racy without non-portable locking...
   end