diff --git a/lib/uri/rfc2396_parser.rb b/lib/uri/rfc2396_parser.rb
index cefd126..b0176a0 100644
--- a/lib/uri/rfc2396_parser.rb
+++ b/lib/uri/rfc2396_parser.rb
@@ -97,7 +97,7 @@ class RFC2396_Parser
     #   u1.eql?(u2) #=> false
     #
     def initialize(opts = {})
-      @pattern = initialize_pattern(opts)
+      @pattern = initialize_pattern(opts.transform_values(&:dup))
       @pattern.each_value(&:freeze)
       @pattern.freeze
 
diff --git a/test/uri/test_parser.rb b/test/uri/test_parser.rb
index c14824f..78ba8da 100644
--- a/test/uri/test_parser.rb
+++ b/test/uri/test_parser.rb
@@ -7,6 +7,19 @@ def uri_to_ary(uri)
     uri.class.component.collect {|c| uri.send(c)}
   end
 
+
+  def test_rfc2396_parser_preserves_options
+    escaped = "%[0-9a-fA-F]{2}"
+    options = {ESCAPED: escaped}
+
+    parser = URI::RFC2396_Parser.new(options)
+
+    assert_equal({ESCAPED: escaped}, options)
+    assert_equal(false, escaped.frozen?)
+    assert_equal("http://example.test/a%20b", parser.parse("http://example.test/a%20b").to_s)
+    assert_nothing_raised { URI::RFC2396_Parser.new(options.freeze) }
+  end
+
   def test_inspect
     assert_match(/URI::RFC2396_Parser/, URI::RFC2396_Parser.new.inspect)
     assert_match(/URI::RFC3986_Parser/, URI::Parser.new.inspect)