diff --git a/lib/uri/common.rb b/lib/uri/common.rb
index cf93fb1..fe8475f 100644
--- a/lib/uri/common.rb
+++ b/lib/uri/common.rb
@@ -46,9 +46,15 @@ def self.parser=(parser = RFC3986_PARSER)
   self.parser = RFC3986_PARSER
 
   def self.const_missing(const)
-    if value = RFC2396_PARSER.regexp[const]
+    if const == :REGEXP
+      warn "URI::REGEXP is obsolete. Use URI::RFC2396_REGEXP explicitly.", uplevel: 1 if $VERBOSE
+      URI::RFC2396_REGEXP
+    elsif value = RFC2396_PARSER.regexp[const]
       warn "URI::#{const} is obsolete. Use RFC2396_PARSER.regexp[#{const.inspect}] explicitly.", uplevel: 1 if $VERBOSE
       value
+    elsif value = RFC2396_Parser.const_get(const)
+      warn "URI::#{const} is obsolete. Use RFC2396_Parser::#{const} explicitly.", uplevel: 1 if $VERBOSE
+      value
     else
       super
     end
diff --git a/test/uri/test_common.rb b/test/uri/test_common.rb
index bccdeaf..176efb8 100644
--- a/test/uri/test_common.rb
+++ b/test/uri/test_common.rb
@@ -13,8 +13,12 @@ def teardown
   def test_fallback_constants
     orig_verbose = $VERBOSE
     $VERBOSE = nil
-    assert URI::ABS_URI
+
     assert_raise(NameError) { URI::FOO }
+
+    assert_equal URI::ABS_URI, URI::RFC2396_PARSER.regexp[:ABS_URI]
+    assert_equal URI::PATTERN, URI::RFC2396_Parser::PATTERN
+    assert_equal URI::REGEXP, URI::RFC2396_REGEXP
   ensure
     $VERBOSE = orig_verbose
   end