diff --git a/test/ripper/test_files.rb b/test/ripper/test_files.rb
index 2bbe4a0060..f30ee8ad2a 100644
--- a/test/ripper/test_files.rb
+++ b/test/ripper/test_files.rb
@@ -12,9 +12,12 @@ class TestRipper_Generic < Test::Unit::TestCase
     SCANNER_EVENTS.each {|n| eval "def on_#{n}(*args) r = [:#{n}, *args]; r.inspect; Object.new end" }
   end
 
+  TEST_RATIO = 0.05
+
   def test_parse_files
     Find.find("#{SRCDIR}/lib", "#{SRCDIR}/ext", "#{SRCDIR}/sample", "#{SRCDIR}/test") {|n|
       next if /\.rb\z/ !~ n || !File.file?(n)
+      next if TEST_RATIO < rand
       assert_nothing_raised("ripper failed to parse: #{n.inspect}") { Parser.new(File.read(n)).parse }
     }
   end