diff --git a/lib/rubygems/mirror.rb b/lib/rubygems/mirror.rb
index 1e0af5e..024ef94 100644
--- a/lib/rubygems/mirror.rb
+++ b/lib/rubygems/mirror.rb
@@ -45,7 +45,7 @@ def update_specs
       path = to(sf)
 
       @fetcher.fetch(from(sfz), specz)
-      open(path, 'wb') { |f| f << Gem::Util.gunzip(File.binread(specz)) }
+      File.open(path, 'wb') { |f| f << Gem::Util.gunzip(File.binread(specz)) }
     end
   end