Index: lib/rubygems/indexer.rb
===================================================================
--- lib/rubygems/indexer.rb	(revision 1)
+++ lib/rubygems/indexer.rb	(working copy)
@@ -116,7 +116,7 @@
     open @specs_index, 'wb' do |io|
       specs = index.sort.map do |_, spec|
         platform = spec.original_platform
-        platform = Gem::Platform::RUBY if platform.nil? or platform.empty?
+        platform = Gem::Platform::RUBY if platform.nil? or platform.to_s.empty?
         [spec.name, spec.version, platform]
       end
 
@@ -130,7 +130,7 @@
     open @latest_specs_index, 'wb' do |io|
       specs = index.latest_specs.sort.map do |spec|
         platform = spec.original_platform
-        platform = Gem::Platform::RUBY if platform.nil? or platform.empty?
+        platform = Gem::Platform::RUBY if platform.nil? or platform.to_s.empty?
         [spec.name, spec.version, platform]
       end