diff --git a/test/lib/test/unit.rb b/test/lib/test/unit.rb
index 2be96fe600..c092018e16 100644
--- a/test/lib/test/unit.rb
+++ b/test/lib/test/unit.rb
@@ -135,6 +135,7 @@ module Test
       end
 
       def non_options(files, options)
+        @jobserver = nil
         if !options[:parallel] and
           /(?:\A|\s)--jobserver-auth=(\d+),(\d+)/ =~ ENV["MAKEFLAGS"]
           begin