diff --git a/test/rdoc/test_rdoc_generator_json_index.rb b/test/rdoc/test_rdoc_generator_json_index.rb
index f25ee27d5e..06a5ddcd4a 100644
--- a/test/rdoc/test_rdoc_generator_json_index.rb
+++ b/test/rdoc/test_rdoc_generator_json_index.rb
@@ -148,8 +148,9 @@ class TestRDocGeneratorJsonIndex < RDoc::TestCase
     assert_file 'js/search_index.js'
     assert_file 'js/search_index.js.gz'
 
-    gzip = File.open 'js/search_index.js.gz'
-    json = Zlib::GzipReader.new(gzip).read
+    json = File.open('js/search_index.js.gz') {|gzip|
+      Zlib::GzipReader.new(gzip).read
+    }
 
     json =~ /\Avar search_data = /