diff --git a/sanic/router.py b/sanic/router.py
index 0af1d13d..917a6812 100644
--- a/sanic/router.py
+++ b/sanic/router.py
@@ -2,6 +2,7 @@ import re
 from collections import defaultdict, namedtuple
 from collections.abc import Iterable
 from functools import lru_cache
+from types import MappingProxyType
 
 from sanic.exceptions import NotFound, InvalidUsage
 from sanic.views import CompositionView
@@ -11,13 +12,13 @@ Route = namedtuple(
     ['handler', 'methods', 'pattern', 'parameters', 'name', 'uri'])
 Parameter = namedtuple('Parameter', ['name', 'cast'])
 
-REGEX_TYPES = {
+REGEX_TYPES = MappingProxyType({
     'string': (str, r'[^/]+'),
     'int': (int, r'\d+'),
     'number': (float, r'[0-9\\.]+'),
     'alpha': (str, r'[A-Za-z]+'),
     'path': (str, r'[^/].*?'),
-}
+})
 
 ROUTER_CACHE_SIZE = 1024
 
@@ -65,7 +66,7 @@ class Router:
     routes_always_check = None
     parameter_pattern = re.compile(r'<(.+?)>')
 
-    def __init__(self, converters=None):
+    def __init__(self, converters=REGEX_TYPES):
         self.routes_all = {}
         self.routes_names = {}
         self.routes_static_files = {}
@@ -73,9 +74,7 @@ class Router:
         self.routes_dynamic = defaultdict(list)
         self.routes_always_check = []
         self.hosts = set()
-        self._converters = REGEX_TYPES
-        if converters:
-            self._converters.update(converters)
+        self._converters = dict(converters)
 
     def parse_parameter_string(self, parameter_string):
         """Parse a parameter string into its constituent name, type, and
diff --git a/tests/test_routes.py b/tests/test_routes.py
index 23c5ca83..aaed2df7 100644
--- a/tests/test_routes.py
+++ b/tests/test_routes.py
@@ -1,11 +1,12 @@
 import asyncio
-import pytest
 import uuid
 
+import pytest
+
 from sanic import Sanic
-from sanic.response import text
-from sanic.router import RouteExists, RouteDoesNotExist, Router
 from sanic.constants import HTTP_METHODS
+from sanic.response import text
+from sanic.router import RouteExists, RouteDoesNotExist, Router, REGEX_TYPES
 
 
 # ------------------------------------------------------------ #
@@ -886,3 +887,25 @@ def test_custom_route_converters():
 
     assert response.text == 'OK'
     assert isinstance(results[0], uuid.UUID)
+
+
+def test_extend_default_rules():
+    regex = r'[A-Fa-f0-9]{8}-[A-Fa-f0-9]{4}-' \
+            r'[A-Fa-f0-9]{4}-[A-Fa-f0-9]{4}-[A-Fa-f0-9]{12}'
+    rules = dict(REGEX_TYPES)
+    rules.update({
+        "uuid": (uuid.UUID, regex)
+    })
+    custom_router = Router(converters=rules)
+    app = Sanic('test_custom_route_converters', router=custom_router)
+    results = []
+
+    @app.route('/<id:uuid>')
+    async def handler(request, id):
+        results.append(id)
+        return text('OK')
+
+    request, response = app.test_client.get('/e010dcb8-6b40-11e7-8e04-0242ac120022')
+
+    assert response.text == 'OK'
+    assert isinstance(results[0], uuid.UUID)