diff --git a/lib/envutil.rb b/lib/envutil.rb
index ab5e8d8..fef9a0c 100644
--- a/lib/envutil.rb
+++ b/lib/envutil.rb
@@ -225,7 +225,8 @@ def invoke_ruby(args, stdin_data = "", capture_stdout = false, capture_stderr =
 
     args = [args] if args.kind_of?(String)
     # use the same parser as current ruby
-    if args.none? { |arg| arg.start_with?("--parser=") }
+    if (args.none? { |arg| arg.start_with?("--parser=") } and
+        /^ +--parser=/ =~ IO.popen([rubybin, "--help"], &:read))
       args = ["--parser=#{current_parser}"] + args
     end
     pid = spawn(child_env, *precommand, rubybin, *args, opt)