diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index 823b64692c..a8e8f9b6f2 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -3,11 +3,13 @@ require_relative 'envutil'
 
 class TestSyntax < Test::Unit::TestCase
   def test_syntax
+    assert_separately %w[--disable-gem], __FILE__, __LINE__, <<-'eom'
     assert_nothing_raised(Exception) do
       for script in Dir[File.expand_path("../../../{lib,sample,ext,test}/**/*.rb", __FILE__)].sort
         assert_valid_syntax(IO::read(script), script)
       end
     end
+    eom
   end
 
   def test_must_ascii_compatible