diff --git a/lib/retest/runner.rb b/lib/retest/runner.rb
index e02c6f9..272ba8d 100644
--- a/lib/retest/runner.rb
+++ b/lib/retest/runner.rb
@@ -98,7 +98,7 @@ def sync(added:, removed:)
 
     def system_run(command)
       log("\n")
-      @pid = spawn(command)
+      @pid = spawn(command, err: File::NULL)
       Process.wait
       @pid = nil
       result = $?.exitstatus&.zero? ? :tests_pass : :tests_fail