diff --git a/addons/http_routing/models/ir_http.py b/addons/http_routing/models/ir_http.py
index 650de9ad74d..c2b8c92197f 100644
--- a/addons/http_routing/models/ir_http.py
+++ b/addons/http_routing/models/ir_http.py
@@ -99,8 +99,9 @@ def slug(value):
     return f"{slugname}-{identifier}"
 
 
-# NOTE: as the pattern is used as it for the ModelConverter (ir_http.py), do not use any flags
+# NOTE: the second pattern is used for the ModelConverter, do not use nor flags nor groups
 _UNSLUG_RE = re.compile(r'(?:(\w{1,2}|\w[A-Za-z0-9-_]+?\w)-)?(-?\d+)(?=$|\/|#|\?)')
+_UNSLUG_ROUTE_PATTERN = r'(?:(?:\w{1,2}|\w[A-Za-z0-9-_]+?\w)-)?(?:-?\d+)(?=$|\/|#|\?)'
 
 
 def unslug(s):
@@ -248,13 +249,13 @@ class ModelConverter(ir_http.ModelConverter):
     def __init__(self, url_map, model=False, domain='[]'):
         super(ModelConverter, self).__init__(url_map, model)
         self.domain = domain
-        self.regex = _UNSLUG_RE.pattern
+        self.regex = _UNSLUG_ROUTE_PATTERN
 
     def to_url(self, value):
         return slug(value)
 
     def to_python(self, value):
-        matching = re.match(self.regex, value)
+        matching = _UNSLUG_RE.match(value)
         _uid = RequestUID(value=value, match=matching, converter=self)
         record_id = int(matching.group(2))
         env = api.Environment(request.cr, _uid, request.context)