diff --git a/test/rubygems/test_gem_ext_builder.rb b/test/rubygems/test_gem_ext_builder.rb
index f03b009c57..abd33d237a 100644
--- a/test/rubygems/test_gem_ext_builder.rb
+++ b/test/rubygems/test_gem_ext_builder.rb
@@ -47,7 +47,7 @@ install:
       Gem::Ext::Builder.make @dest_path, results
     end
 
-    results = results.join "\n"
+    results = results.join("\n").b
 
     assert_match %r{"DESTDIR=#{ENV['DESTDIR']}" clean$},   results
     assert_match %r{"DESTDIR=#{ENV['DESTDIR']}"$},         results
@@ -78,7 +78,7 @@ install:
       Gem::Ext::Builder.make @dest_path, results
     end
 
-    results = results.join "\n"
+    results = results.join("\n").b
 
     assert_match %r{"DESTDIR=#{ENV['DESTDIR']}" clean$},   results
     assert_match %r{"DESTDIR=#{ENV['DESTDIR']}"$},         results