2 files changed, 13 insertions, 1 deletions
diff --git a/regexec.c b/regexec.c
index 140691ad42..6d82429e03 100644
--- a/regexec.c
+++ b/regexec.c
@@ -4218,7 +4218,8 @@ match_at(regex_t* reg, const UChar* str, const UChar* end,
 
  timeout:
   xfree(xmalloc_base);
-  xfree(stk_base);
+  if (stk_base != stk_alloc || IS_NOT_NULL(msa->stack_p))
+      xfree(stk_base);
   HANDLE_REG_TIMEOUT_IN_MATCH_AT;
 }
 
diff --git a/test/ruby/test_regexp.rb b/test/ruby/test_regexp.rb
index c996b1785a..03d96954b4 100644
--- a/test/ruby/test_regexp.rb
+++ b/test/ruby/test_regexp.rb
@@ -1827,6 +1827,17 @@ class TestRegexp < Test::Unit::TestCase
     end;
   end
 
+  def test_bug_20453
+    assert_separately([], "#{<<-"begin;"}\n#{<<-'end;'}")
+    begin;
+      Regexp.timeout = 0.001
+
+      assert_raise(Regexp::TimeoutError) do
+        /^(a*)x$/ =~ "a" * 1000000 + "x"
+      end
+    end;
+  end
+
   def per_instance_redos_test(global_timeout, per_instance_timeout, expected_timeout)
     assert_separately([], "#{<<-"begin;"}\n#{<<-'end;'}")
       global_timeout = #{ EnvUtil.apply_timeout_scale(global_timeout).inspect }