diff --git a/test/ruby/test_regexp.rb b/test/ruby/test_regexp.rb
index 812ecce905..828117f516 100644
--- a/test/ruby/test_regexp.rb
+++ b/test/ruby/test_regexp.rb
@@ -1929,7 +1929,7 @@ class TestRegexp < Test::Unit::TestCase
   end
 
   def test_match_cache_positive_look_ahead
-    assert_separately([], "#{<<-"begin;"}\n#{<<-'end;'}")
+    assert_separately([], "#{<<-"begin;"}\n#{<<-'end;'}", timeout: 30)
       timeout = #{ EnvUtil.apply_timeout_scale(10).inspect }
     begin;
        Regexp.timeout = timeout