diff --git a/aiopenapi3/openapi.py b/aiopenapi3/openapi.py
index 2e31437c..24f877e6 100644
--- a/aiopenapi3/openapi.py
+++ b/aiopenapi3/openapi.py
@@ -492,6 +492,7 @@ def url(self):
 
             if self._root.host:
                 host, _, port = self._root.host.partition(":")
+                port = None if port == "" else port
             else:
                 host, port = base.host, base.port