diff --git a/sample/test.rb b/sample/test.rb
index b1560d3105..f3ac9c4a49 100644
--- a/sample/test.rb
+++ b/sample/test.rb
@@ -1931,7 +1931,7 @@ end
 def valid_syntax?(code, fname)
   p fname
   code = code.dup.force_encoding("ascii-8bit")
-  code.sub!(/\A(\xef\xbb\xbf)?(\s*\#.*$)*(\n)?/n) {
+  code.sub!(/\A(?:\xef\xbb\xbf)?(\s*\#.*$)*(\n)?/n) {
     "#$&#{"\n" if $1 && !$2}BEGIN{throw tag, :ok}\n"
   }
   code.force_encoding("us-ascii")
diff --git a/test/ruby/test_system.rb b/test/ruby/test_system.rb
index 2143fcad71..be441c95fe 100644
--- a/test/ruby/test_system.rb
+++ b/test/ruby/test_system.rb
@@ -5,7 +5,7 @@ require_relative 'envutil'
 class TestSystem < Test::Unit::TestCase
   def valid_syntax?(code, fname)
     code = code.dup.force_encoding("ascii-8bit")
-    code.sub!(/\A(\xef\xbb\xbf)?(\s*\#.*$)*(\n)?/n) {
+    code.sub!(/\A(?:\xef\xbb\xbf)?(\s*\#.*$)*(\n)?/n) {
       "#$&#{"\n" if $1 && !$2}BEGIN{throw tag, :ok}\n"
     }
     code.force_encoding("us-ascii")