diff --git a/lib/minitest/assertions.rb b/lib/minitest/assertions.rb
index da07b00e..8941cebd 100644
--- a/lib/minitest/assertions.rb
+++ b/lib/minitest/assertions.rb
@@ -565,6 +565,11 @@ def capture_subprocess_io
           captured_stderr.unlink
           $stdout.reopen orig_stdout
           $stderr.reopen orig_stderr
+
+          orig_stdout.close
+          orig_stderr.close
+          captured_stdout.close
+          captured_stderr.close
         end
       end
     end