diff --git a/lib/rubygems/specification.rb b/lib/rubygems/specification.rb
index 11facfb45c..275483ccc6 100644
--- a/lib/rubygems/specification.rb
+++ b/lib/rubygems/specification.rb
@@ -464,10 +464,7 @@ class Gem::Specification < Gem::BasicSpecification
   #   spec.platform = Gem::Platform.local
 
   def platform=(platform)
-    if @original_platform.nil? ||
-       @original_platform == Gem::Platform::RUBY
-      @original_platform = platform
-    end
+    @original_platform = platform
 
     case platform
     when Gem::Platform::CURRENT then
@@ -1308,7 +1305,7 @@ class Gem::Specification < Gem::BasicSpecification
     spec.instance_variable_set :@summary,                   array[5]
     spec.instance_variable_set :@required_ruby_version,     array[6]
     spec.instance_variable_set :@required_rubygems_version, array[7]
-    spec.instance_variable_set :@original_platform,         array[8]
+    spec.platform =                                         array[8]
     spec.instance_variable_set :@dependencies,              array[9]
     # offset due to rubyforge_project removal
     spec.instance_variable_set :@email,                     array[11]
@@ -1316,8 +1313,6 @@ class Gem::Specification < Gem::BasicSpecification
     spec.instance_variable_set :@description,               array[13]
     spec.instance_variable_set :@homepage,                  array[14]
     spec.instance_variable_set :@has_rdoc,                  array[15]
-    spec.instance_variable_set :@new_platform,              array[16]
-    spec.instance_variable_set :@platform,                  array[16].to_s
     spec.instance_variable_set :@licenses,                  [array[17]]
     spec.instance_variable_set :@metadata,                  array[18]
     spec.instance_variable_set :@loaded,                    false
@@ -1813,15 +1808,16 @@ class Gem::Specification < Gem::BasicSpecification
   def encode_with(coder) # :nodoc:
     coder.add "name", @name
     coder.add "version", @version
-    platform = case @original_platform
+    platform = case @new_platform
                when nil, "" then
                  "ruby"
                when String then
-                 @original_platform
+                 @new_platform
                else
-                 @original_platform.to_s
+                 @new_platform.to_s
     end
     coder.add "platform", platform
+    coder.add "original_platform", @original_platform.to_s if platform != @original_platform.to_s
 
     attributes = @@attributes.map(&:to_s) - %w[name version platform]
     attributes.each do |name|
@@ -2626,13 +2622,12 @@ class Gem::Specification < Gem::BasicSpecification
       when "date"
         # Force Date to go through the extra coerce logic in date=
         self.date = val
+      when "platform"
+        self.platform = val
       else
         instance_variable_set "@#{ivar}", val
       end
     end
-
-    @original_platform = @platform # for backwards compatibility
-    self.platform = Gem::Platform.new @platform
   end
 
   ##
diff --git a/test/rubygems/test_gem_package.rb b/test/rubygems/test_gem_package.rb
index 2065864107..8a9cc85580 100644
--- a/test/rubygems/test_gem_package.rb
+++ b/test/rubygems/test_gem_package.rb
@@ -438,6 +438,33 @@ class TestGemPackage < Gem::Package::TarTestCase
     assert_equal %w[lib/code.rb], reader.contents
   end
 
+  def test_build_modified_platform
+    spec = quick_gem "a", "1" do |s|
+      s.files = %w[lib/code.rb]
+      s.platform = Gem::Platform.new "x86_64-linux"
+    end
+
+    spec.platform = Gem::Platform.new "java"
+
+    FileUtils.mkdir "lib"
+
+    File.open "lib/code.rb", "w" do |io|
+      io.write "# lib/code.rb"
+    end
+
+    package = Gem::Package.new spec.file_name
+    package.spec = spec
+
+    package.build
+
+    assert_path_exist spec.file_name
+
+    reader = Gem::Package.new spec.file_name
+    assert reader.verify
+
+    assert_equal spec, reader.spec
+  end
+
   def test_raw_spec
     data_tgz = util_tar_gz {}