diff --git a/lib/uri/common.rb b/lib/uri/common.rb
index a4ed70f9a3..98cb18ec0d 100644
--- a/lib/uri/common.rb
+++ b/lib/uri/common.rb
@@ -27,8 +27,10 @@ module URI
     const_set("Parser", parser.class)
 
     remove_const(:REGEXP) if defined?(REGEXP)
+    remove_const(:PATTERN) if defined?(PATTERN)
     if Parser == RFC2396_Parser
       const_set("REGEXP", URI::RFC2396_REGEXP)
+      const_set("PATTERN", URI::RFC2396_REGEXP::PATTERN)
       Parser.new.pattern.each_pair do |sym, str|
         unless REGEXP::PATTERN.const_defined?(sym)
           REGEXP::PATTERN.const_set(sym, str)
diff --git a/test/uri/test_common.rb b/test/uri/test_common.rb
index 8d0a206c86..aa9c6898ed 100644
--- a/test/uri/test_common.rb
+++ b/test/uri/test_common.rb
@@ -12,17 +12,21 @@ class URI::TestCommon < Test::Unit::TestCase
 
   def test_parser_switch
     assert_equal(URI::Parser, URI::RFC3986_Parser)
-    refute defined?(::URI::REGEXP)
+    refute defined?(URI::REGEXP)
+    refute defined?(URI::PATTERN)
 
     URI.parser = URI::RFC2396_PARSER
 
     assert_equal(URI::Parser, URI::RFC2396_Parser)
     assert defined?(URI::REGEXP)
+    assert defined?(URI::PATTERN)
+    assert defined?(URI::PATTERN::ESCAPED)
 
     URI.parser = URI::RFC3986_PARSER
 
     assert_equal(URI::Parser, URI::RFC3986_Parser)
     refute defined?(URI::REGEXP)
+    refute defined?(URI::PATTERN)
   ensure
     URI.parser = URI::RFC3986_PARSER
   end