Index: test/uri/test_generic.rb
===================================================================
--- test/uri/test_generic.rb	(revision 31234)
+++ test/uri/test_generic.rb	(working copy)
@@ -696,6 +696,12 @@ class URI::TestGeneric < Test::Unit::Tes
     assert_raise(URI::InvalidURIError) { uri.query = 'bar' }
   end
 
+  def test_set_scheme
+    uri = URI.parse 'HTTP://example'
+
+    assert_equal 'http://example', uri.to_s
+  end
+
   def test_ipv6
     assert_equal("[::1]", URI("http://[::1]/bar/baz").host)
     assert_equal("::1", URI("http://[::1]/bar/baz").hostname)
Index: lib/uri/generic.rb
===================================================================
--- lib/uri/generic.rb	(revision 31234)
+++ lib/uri/generic.rb	(working copy)
@@ -272,7 +272,7 @@ module URI
     private :check_scheme
 
     def set_scheme(v)
-      @scheme = v
+      @scheme = v ? v.downcase : v
     end
     protected :set_scheme