diff --git a/lib/rubygems/remote_fetcher.rb b/lib/rubygems/remote_fetcher.rb
index dbd4cef..3926a85 100644
--- a/lib/rubygems/remote_fetcher.rb
+++ b/lib/rubygems/remote_fetcher.rb
@@ -88,7 +88,9 @@ class Gem::RemoteFetcher
 
    # Always escape URI's to deal with potential spaces and such
     unless URI::Generic === source_uri
-      source_uri = URI.parse(URI.escape(source_uri))
+      source_uri = URI.parse(URI.const_defined?(:DEFAULT_PARSER) ?
+                             URI::DEFAULT_PARSER.escape(source_uri) :
+                             URI.escape(source_uri))
     end
 
     scheme = source_uri.scheme